I've been to Key West twice, and I liked it even less the second time. It's a tourist trap, in my opinion. But I'm sure some people love it.

Forget Hawaii using miles.
I got a 30Kmi Delta voucher last Dec which specifically states that it's good for one year to HI, but they changed the fee in March to 35Kmi and no FF seats are available mid Nov - mid Jan. Also, Delta had no 30K mi seats to St. Thomas (USVI) last Jan, but would let you have one for 60K mi.
I used my AA miles - their 757s are marginally better than anything Delta flys, and AA's 757s have the worst coach seats in their fleet (we scored exit seats RT San Juan to DFW which helped). A recent Delta 737...coach flight DFW-SAN was awful as three hours in coach is my limit.
M

My husband travels alot, and has some miles, and I've been to Hawaii 4 times in three years using miles. I've never had a problem getting FF seats. I call about 5-6 months in advance give my date and I get seats.
One Hawaii trip I used Miles for airfare, Hilton Points for the room, and points for the week car rental! We went all out on food and drink, because everything else was 'paid for'!
I LOVE MILES!

If you have a ton of miles, convert them into Hilton Points and stay for 'free' too.....and they have car rentals for 'free' too.

If you have family, miles are great to have saved up should you have to fly somewhere at the last minute for a funeral or event. Last minute fares can run from $600 to $1200. It would be silly to waste miles on a $200 roundtrip.

Then again, if Northwest goes out of business the miles might be worthless.