My husband and I are going to vegas for a wedding the end of Jan. We had planned to rent a car and drive to SD. We will leave vegas Tues and fly out of SD sat or sun. I was looking for some interesting routes and scenic places to go through and maybe stop for a day. My husband wants to drive through LA as well.

In January, it will be around 70-75 degrees, if not warmer, sunny and beautiful here. Make a stop in Palm Springs on your way - perfect time of year.

If you go to Palm Springs, here's a fun, scenic drive over to SD... Take 10 east and get on route 86 (I think east, but you'll be heading south) towards the Salton Sea. Then you can take route S22 into Anza-Borrego Desert State Park - it's a beautiful drive down into Borrego Springs. And from Borrego Springs, head to Julian - it's a cute little one-horse gold-mining town...

If you don't go to Palm Springs, it's also nice to stop in Temecula, CA. This is on the way on I-15 from Vegas to SD. If you're into wine-tasting, there are some decent wineries in Temecula. From there, you can head directly over to the coast and drive down the coast into SD.

I did the reverse trip back in April and we stopped for a night in Palm Springs. This gave us time to go up the Aerial Tramway in Palm Springs and explore Joshua Tree National Park (one of my favourites). Joshua Tree is positioned between Las Vegas amd Palm Springs.

We also stopped in Pioneertown (not far from one of the Joshua Tree NP entrances) for a meal at Pappy and Harriet's. Pioneertown (www.pioneertown.com - an old town where some Western films were made and it looks like it's barely changed since then).

The only other time I have done the drive from San Diego to Las Vegas was straight along the I-15 and that was pretty boring so you're wise to want to make it more interesting. I'd rather fly than do the I-15 drive again.

palm springs would be a nice place to stop for a night. leave vegas early so you have time to explore palm springs a bit. from palm springs, it's on 2 1/4 hours to san diego. january is the worst month for weather for that area though so you may run into some rain.
otherwise, just drive straight to san diego. plenty to keep you busy there for 4 days.
i'm not sure why your husband wants to drive through la but i would advise against it. it's a total drag driving through that city and if you hit a traffic jam, you could easily waste 1-3 hours sitting in traffic. if you do decide to go that route though, stop in laguna beach between la & san diego. nice little town.