Lovely Kiwis,
Frankly, four days to do this route is like a forced march. There would be few "must-sees" on this trip because you would be spending 10 hours/day in your car and the gas stations.
The distances are much to long to get any enjoyment out of it.

If I were you, if you HAVE to fly into Las Vegas (the Visitors' Bureau there must be selling this up a storm overseas; I have never seen so many people going to Las Vegas for vague reasons and having no idea how far it is away from California, and how god-awful hot it is there in the summer)
I would fly from Las Vegas to San Francisco, do not rent a car, spend 3 days time in SF, then rent a car later and make a day drive down Highway 1 on the Pacific Ocean, as far as you have time left - Half Moon Bay if necessary, or evem better, Carmel/Monterey if you have time.
There must be some fascination with deserts out there (Furnace Creek) but summer is not the time to go, it should be early spring. It is 120 degrees Fahrenheit in Death Valley, and at night it can be 90 degrees all night.
Unless you have family in Bakersfield, it's definitely not the place to stop overnight. Plain vanilla has nothing on this bleak town. Its claim to fame is oil and Merle Haggard, the country singer.

I agree,. It is much too hot to go into Death Valley from Las Vegas in July. Drive your LV rental car to see Red Rocks, Valley of Fire, Hoover Dam and the South Rim of the Grand Canyon. Return the car and fly to SFO or Oakland and rent another car. The only other way to get from LV to San Francisco is to Take the Amtrak bus from the bus station near Fremont St. to Bakersfield to get on the San Joaquin train all the way to Emeryville. At Emeryville you have the choice of taking an Amtrak bus into the city of San Francisco or renting a car.

IF Death Valley (in August!) was a must and IF taking the car was a must, I'd probably go thru Yosemite after "enjoying" Death Valley. Just make sure you read the informations and advice on traveling thru the deserts, fill up gas, and take water with you (not just a little bottle that fits in a cupholder, but rather a big one gallon bottle). http://www.nps.gov/deva/index.htm

Or veer off the direct route a bit to the north on 395 to Tahoe, go west on 50. And include a stop in Sacramento.
You'd get at least a pretty diverse mix of California landscapes, from deserts to mountains.

But, after all, the aforementioned variation to fly to the Bay Area and rent a car from SF to explore the coast south ot north of the city still sounds like the better option..

I love Death Valley but NEVER in the summer!! It is dangerously hot in August, and it can hurt to breathe. It will not be enjoyable at all. The driving distances are long with nothing in between. Las Vegas is miserably hot, too, but at least you can stay in air conditioned buildings. Book a flight on Southwest Airlines from Las Vegas to San Francisco. It tends to be the lowest cost airline. Then you can spend your driving time enjoying great places in Northern California. If you insist on going through Death Valley, drive as Cowboy1968 suggested - up Hwy 395 and then west on Hwy 50 to Hwy 80 to San Francisco.

If you do go to DV, take some eggs. You can cook them by putting them on the rocks.

DV weather Auguast. http://gocalifornia.about.com/bl_dv_temp.htm

DV is not a good place to die. Even the buzzards won't go out in this weather.

What about driving to Los Angeles/Hollywood and then up the coast? Are you seeing L.A. at a different point in your travels?

Also, if you haven't already "pre paid" your car rental, on some days of the week there are very inexpensive flights from LV to Santa Maria Ca. From Santa Maria you can have a nice time driving up through Pismo, Shell Beach, Avila, San Luis Obispo, Morro Bay, San Simeon, Cambria, Carmel, Monterey etc.

Hi, Kiwis.

Sorry for the somewhat belated response. IMO, your outlined route is quite doable, and I have some suggestions relating to that, which I will post separately after this. But first, I want to address the issue of Death Valley, which drew several negative comments, mostly centered on the high temperatures to be expected in the summer. (I suspect you already knew that.)

I suggest you visit the National Park Service Death Valley Website

http://www.nps.gov/deva/index.htm

It's an objective source of info that will make your (brief} visit there more enjoyable.

Quote from the NPS Website

"SUMMER starts early in Death Valley. By May the valley is too hot for most visitors, yet throughout the hottest months, visitors from around the world still FLOCK to the park. (Caps mine). Lodging and camping are available, but only the most hardy will want to camp in the low elevations in the summer. Most summer visitors tour by car to the main points of interest along the paved roads but do little else due to the extreme heat. Those wanting to hike will find the trails to Telescope and Wildrose Peaks are at their best in summer, but it is best to wait."

Quote from the Sacramento Bee.

"The number of people visiting Death Valley in the summer, when temperatures often exceed 120 degrees, has soared from 97,000 in 1985 to 257,500 in 2009. That pattern holds at Joshua Tree as well, which recorded 128,000 visitors in the summer of 1988. Last year: 230,000."

From the NPS FAQs.
Is it safe to visit Death Valley in the summer?

Yes, but you must be prepared and use common sense. With an air conditioned vehicle you can safely tour many of the main sites in Death Valley. Stay on paved roads in summer, and if your car breaks down, stay with it until help arrives.
Always bring plenty of water in your car in case of emergency and drink at least 2 to 4 liters per day, more if you are active in the heat. Summer hiking is not recommended except in the early morning hours and in the mountains.

Also from the NPS FAQs.
I only have two hours to visit Death Valley, what should I see?

The most popular drive in Death Valley is the Badwater Road. If you visit the Devil’s Golf Course, Badwater, and take Artist's Drive on the return trip back to Highway 190 it should take about 1½ hours round-trip. Add a stop at Zabriskie Point if you are continuing east, or stop at the sand dunes if you are heading west to round out your 2 hour visit.

My recommendation: Since you will already be close by in Las Vegas, by all means spend a few hours in Death Valley. It's scenic values outweigh the brief discomfort you will feel due to the heat. And, as you can see by the attendance numbers, you will not be alone.

Death Valley was aptly named and it's really nothing but burnt rock - and seeing it once is fine but would not put it at the top of your list for this trip. We went through in early summer - and it was hot - 113 in the shade at the Visitor's center at about 1 PM and going up.

As Tomf suggested - much better to drive or take a tour over to the incredible Grand Canyon - and then visit Red Rock Canyon (20 minutes outside of Vegas) - and then fly to San Francisco - and drive partway down the coast from there - say as far as Big Sur - easily doable in a day - although would recommend you try and spend a night in the area - and enjoy the Aquarium and Cannery row in nearby Monterrey - and also the 17 mile drive in Camel/Pebble Beach.

Another way to reach SF, which might be more interesting because you have plenty of coast in New Zealand:

Drive up US95 in Nevada and then take NV266 to CA 168. On the way you'll go over a pass which has a turn-off to a bristlecone pine forest. CA168 to US395, go north to Bodie State Historic Park (a mining ghost town). Go over the Sierra either via Tioga Pass into Yosemite or farther north on CA 108 to visit Columbia State Historic Park. Then west to San Francisco.

About driving in Death Valley. I have a European relative who dreamt of driving in Death Valley in the middle of summer in a convertible. He had to settle for a hard top with the windows open. To each his own.