Think about how you want to use the coach. Do you want to go just to warm climates? Or do you want to also use it in cold climates? If you are going to use it in cold climates you'll want a coach with an enclosed basement rather than the boxes that travel out on the slides.
We previously had a 2005 Excursion 39L and a 2008 35' Southwind.
Older units often have fewer power plugs, and will have older electronics (TV's, etc.)
If you get slides, check for air gaps when the slide is out. Not a huge deal if you're only using in warmer weather, but our 2005 Excursion was a big problem in cold climates. We were stuffing rolled up beach towels around the slides to block the drafts in winter while going snow skiing.
Some of the things (less obvious) that I'd pay attention to now:
1. Width of the entry door. You're going to go in and out carrying stuff, etc. Some of the units are narrower.
2. Furniture height. My wife is short....some of the furniture she can't get her feet on the floor. Sounds funny, but when your legs dangle and go to sleep, not so much.
3. Access to controls...what can you reach and what can't you reach from the driver's seat?
4. Dash gauge colors....sounds silly, but I'm over 50, and have trouble reading the white letters on a black background during the day with sunglasses on in bright light.
5. Towing capacity
6. Location of fuel filler. The 35' Southwind was gas powered, and the filler is on the back. It was sometimes difficult to get into fuel islands when pulling a vehicle, and truck lanes aren't an option for a gas engine.
7. Check the date codes on the tires! You may find units out there in the age range you're looking at with original tires. If so, they will need to be replaced.
Those are the things that come to mind....