Fiberglass and polyester resin = problem
but the true epoxy resins aren't as easily affected. Lining the fiberglass tank isn't terrible and it is commonly done.
even still, the fiberglass tank would fetch more than $250-300 wouldn't it? Not that you would necessarily sell it.
Being fiberglass components it gives you options if you would want to go to another look like the parade tanks or otherwise. Clean them up before you strip it down so it looks nicer and you have photos showing the assembled components. It will bring better money if you decide to sell them. I think the current package as shown goes together well and with a fresh paint scheme that is colorful it would look much nicer. It is unique and shouldn't it fetch more than what a nice R75/5 would go for normally when in near equal condition?
The old BMW bikes are cool I think, if it is in good shape mechanically and had a good rebuild, then it would be worth buying and fixing up. Just about any bike you can expect to spend 400-500 on new tires, bearings, filters, and other sundries. Do your own paintwork and you have added another $250-400.
Patience grasshopper, just don't get too emotionally attached to this one yet.
Terry, nice bike.