The 25" tire will only raise the rear 1" higher versus the stock 23". I think that the sidewall wrinkling issue is probably related more to the tire carcass construction than the bike being too heavy for the size.
The greatest advantage I have found is that the bigger tire allows a higher top speed while retaining the stock gearing. I haven't found a secondary chain sprocket bigger than a 13 and I don't think you can get anything other than stock for the rear sprocket since it is dished.
There doesn't seem to be a whole lot of aftermarket support for bikes that are 25 years old and were unpopular when they were new.