I usually see rc10gt's go for $125-$200 ish on ebay. $200 would be with upgrades and spare parts. but ebay is funny, you might put it for $100 and not sell it one week, and the next get a bunch of guys bidding and have it go for $200.
while I also much prefer electrics, the rc10gt is a good, simple nitro. Any time that I have had a nitro it has always been a stadium truck, as they are usually the easiest to work on and generally durable.
Basically, I doubt you could sell it for enough to buy a good electric....but selling it would get you at least half way towards buying a decent one.
so it is a toss up. but since you have had it in storage for 3 years, it might be safe to say you would use a electric more
maybe try trading on RCU first...see if you get any interesting offers. just don't trade with anyone who doesn't have a decent amount of feedback.
if that doesn't work, then put it up on ebay for a high price. if it doesn't sell, then try again with a low starting bid.