Is this a good trade?

[persona]

I own a very old acoustic piano (I guess 60 years old) which doesn't sound very well. Also, the keys are very heavy (I compared them with the ones in a good piano, and they are indeed heavier than they should be). That is why I always practice on a casio keyboard (ctk 900). So, if I decided to trade them both for a good electric piano (say, yamaha), maybe adding some money (U$S 400 maybe), would that be wise? I ask this because I would like to practice in the elecrtical piano and then be able to play in an acoustic one without having to start learning the technic all over. Is this possible?
Also, I'd like to know if there are pianos with different weight in their keys, because all the electrical pianos I heard about were described as "semi-heavy". Now, how different would these be from a real acoustic one?