Should I keep buying other domain names?

I run Jeepz.com, which is a nicely growing site. At one point I purchased some other domain names, and began pointing them to jeepz.com (i.e. JeepLinks.com would send you to the main page of Jeepz.com). I noticed that I would have duplicate content listed in google (same pages under different domain names). My understanding now is that google doesn't like this.

I've since stopped this, and have setup another website for jeeplinks. Along the way I've also picked up two more pr2 domain names, and have setup small html sites for them, with some text links to my main site.

What do you guys do with domain names that do get traffic, but you aren't ready / willing to design a comprehensive site for? Should I create a page with limited info, and links to my main site, or just park the domain for the time being? Would this boost my page rank, or hurt it?

If you're going to direct them back to your main site, then you need to properly 301 redirect them. Don't just set them up to access your jeepz.com forum.

The question would be:

Can you recover your domain fees from the traffic that spills over to your forum through ad clicks?

Otherwise, can you resell the domain later at/above your purchase price to recover your investment?

My thought was originally to hold these domains and get rich in 10 years when I sell them! then I had the idea:

why not setup a new site about jeeps with some good info (2 or 3 html pages), some adsense, and several links to my "real" website. Thinking that having this new PR2 site with several links to my main site would boost it's overall traffic and page rank.