I regularly visit about 10 sites a day, spreading spam like avian flu. I can tell you most sites have some kind of limit, like no gallery (pics hosted elsewhere only), small sigs, register only, something. Big sites like rc universe are so loaded with ads that it is slow to upload, and it is just annoying. RCNT is my favorite site, with the best combo of users and user-friendly access.
Here are two suggestions.
1. Create a manufacturer's forum, and charge them a small fee to spam thier brains out. RC Solutions and RAM tech for example, get a hell of a lot of great exposure and free press here at RCNT. Any amount from $20 to 50 a month would be a bargain for a company, and just a few could cover the bills. RC Solutions spends $150 a month for a 750 x 150 rotating banner on one rc site! I try to keep a low profile spam wise (I don't say RC Solutions in my sig for example) so hopefully I can enter general discussions without everyone rolling their eyes and thinking here comes the rc sol shill again. Woodie made me an rcnt affiliate a while back and put up a rc sol banner for free, and I actually asked him to take it down. I would rather have a dedicated forum for advertising, so that viewers can go there on purpose to get spammed, rather than drown in it like rcuniverse. RC revolution has a good example of a manufacturers forum, but they are a site that requires you to register to view.
2. Limit pic size in a post to 20k or less, and gallery images to 640x480. Other sites make no bones about not hosting pics at all, so it is not unreasonable to have a limit on file size.
RCNT is a victim of its own success! There are worse problems to have.