They're not hard to maintain, it's more like a stream of constant maintenance. But aside from fixing rust, which does require a lot of skill, the mechanicals are simple and parts aren't terribly expensive. Definitely fun vehicles, but I wouldn't get one if I wasn't mechanically inclined or unwilling to learn how to work on it, or lacked the time and space to work on it. They're 40 year old vehicles that have taken a lot of abuse over their lives, so more often than not they're total basket cases that require a lot of attention. It really makes you appreciate how maintenance free a modern vehicle is. It's a slow sort of revival with mine. I'm stuck in an apartment for a year, and can't find a space to work on it, so I can only do so much. Eventually I'll really be able to tear into it. On a more positive note, there are few things better than wandering leisurely down the coast in a VW bus on a sunny day. :)
Doesn't fixing rust really just mean cutting the metal away and welding new (sheet metal or otherwise) to the sections of good steel that are exposed? I've got rust round my wheel wells of my current ride, and a little on the window frames. I don't think I really have the tools to take care of it based on what I've read.