Re: Squier Affinity or Fender Mexican which worth upgrade?
There is a huge difference in the neck, IMO. The Mex neck will be meatier, thicker and most importantly, more stable.
As an owner of both a pimped-out Affinity Strat and a half Mex, half American pimped-out Fender Strat, I can tell you that modding a Affinity is going to be fun, and you'll learn a lot, but it's not 100% worth it, unlike the Mex Fender. There's no comparison for me.
However... if your priority is comfort above all things, then I'd go for the Affinity. Doesn't sound to me like you're trying to get an "ultimate" Strat, but rather to learn your way and keep a cool hobby going. So go for it man.