The mex strats are pretty decent to me. I think as long as a guitar plays well, then there's no need for an upgrade.. And in any case, you might find yourself wandering into anotehr minefield if you dunno what kind of sound you're aiming for -- the blues/vintage people might want to upgrade their pups to Fralins, but these might not appeal to rockers who want their active EMGs. So again, it really depends on the sound and feel that you're aiming for... You'll save a lot of money and time if you go out shopping knowing what you want already.
Anyway the Mex Strat is not really a "collectors edition" so don't worry about tweaking it.. i think the collector's era is pretty much over already unless these are really rare, one-off items. Its like, I got a batch of 10 yr old poly-bagged comics that are still worth nothing today... and i feel very sore abt it,..