1. Some of the things to check were listed in a previous post
2. Some people will disagree, but I don't think the upgrades are worth a $20,000 difference. The DMC Florida car partly costs so much more because it is a DMC Florida car. That's about it.
3. I would whole-heartedly say no. The warranty is all well and good, but not worth enough to justify buying the higher priced car (upgrades not withstanding).
I would suggest checking out the cheaper car. The seller may not provide support, but you can still go to DMC Florida to have work done. They will answer all your questions and be a great source to get parts through. I think a stock DeLorean is fine for me, so I don't need Stage 2 or anything. But some people want to push the power of this old car and see where they can take it. LANAAAA! DANGER ZONE.