KaBudokan's right. Just play it.
Buying a run-of-the-mill production Fender as an "investment" ranks right up there with buying a Chevy and garaging it for 20 years. Think about it. Cars are made to be driven, guitars are made to be played.
There's no telling what's going to happen to the value in 20 years anyway. The antiques market is fickle that way. And God forbid it should get stolen, or damaged in a natural disaster, or burned in a fire, or eaten by termites. Meanwhile you get to worry about it for all that time, and you don't even get to enjoy it!
You want an investment, buy art or bonds. You want a guitar that'll be worth serious money in 20 years, get something better than a Fender, or make yourself famous playing the one you have.