Zona,
As InterestedEnough mentioned, I would suggest that you park with a service that allows you to not only customize your domains, but also to promote them (most don't allow this but some do). The results may not be as good as mini sites, but it will also be much less work. You can start by adding the keywords in the domains to the optimization (title, description, and keywords), make sure the domain is showing proper images, and that the links and keywords are ok. Later you can go back and add content or change image/keywords to see if you can get things showing that people will click on. The traffic reports for searches should give you clues or slap you in the face with what you should be using.
Then you can add original (or not) content and cross-link your domains where there are simular topics. You will have to decide when to link to your other domains or a main site, but I tend to wait until the domain has at least some PR. I think it is natural for some crap/no PR sites to link to you, but if there are hundreds... well I don't know. You can also get outside links to your domains (again, if allowed) just like you would for a mini site. Hint: some directories will take listings for parked domains, but some won't.
We have been working on this and have some parked domains that have reached PR4, but not many so far, and it takes 2-3 months to start seeing any PR at all with new domains.
If you have domains and park them on a main domain or site, I don't think you will seem much gain that will last. Perhaps just the traffic/links that each brings. A 301 redirect might be better and I have seen some signs that PR gets passed that way, but no proof. It would be more trouble than it's worth to set up 500 redirects, IMO. I also think the redirect will cause some links to either be changed to point directly or be dropped.
I've been thinking about trying this: Set up a site on a specific topic with lots of content. Point a domain there and get some links to help it be indexed. Leave it that way for 3-6 months. Then park the domain with a parking provider and set it up with the same kind of optimization. Then take another domain and point it towards the site and start the process over again. Yeah, it's kind of an "incubation" process to get things started.