Re: '04 MIM Strat - Upgrading tuners?
I hear ya...Those are over all good guitars, but with a few mods they can become excellent guitars. They really have a hard time staying in tune when stock. It's their biggest weakness IMO (worse than the stock pickups, which I actually think are fairly usable).
The vibrato itself is one culprit. If you never use it, I'd block it down with a piece of wood. If you do use it, I'd lubricate it liberally around the fulcrum, upgrade the saddles, and upgrade the springs with stiffer spring. You can also go with a full-on to a Callaham vibrato replacement, but they're expensive.
The stock nut can be fine if you have it properly slotted. Going to a brand new Tusq XL nut is even better. Again, costs some money, but worth it if it's a guitar you gig with all the time.
As for the tuners, there are drop-in locking tuners made by by Schaller, or the same basic tuners labeled as Fender brand. They drop right into the shaft holes and locating holes on the MIM headstocks. You can also put Sperzels on by drilling six tiny holes (one between each of the stock holes for the locating pins), and they will look stock because all the stock holes will still be hidden. Another option is vintage style locking tuners by Gotoh, installed by way of adapter bushings. That's cool because you get locking tuner performance, but you also get the classic button tuner look.
In any case, however, the tuners are usually the most innocent of those three culprits IMO. Before getting new tuners, get some nut work done, and lubricate and/or upgrade your vibrato unit.