Really depends. What niche? How old are they? I don't have a lot of experience in SEO, so wait for someone that can really answer for you
Yeah - if you're successful it could be a nice benchmark for us. I have never considered buying a "used" domain before...
Not true. Pagerank is completely agnostic. It only ranks the value of valid inbound links and nothing else. Some domains do get dinged down to no PR if they've been dropped for too long. But, as long the inbound links are there and are of good PR themselves, the site's PR will pop back up when Google does the new ranks (approximately every three months).
Where is a good dropped domain site? FreshDrop was great but have started charging for everything now. JustDropped is Ok, but can someone recommend another one?