My question is, should I bother replacing the PCV valve. The 2003 Lancer ES has around ~90k miles on it, and before that is was a rental car - highly doubt it was taken care of properly. So now I'm just replacing small parts I know how to replace/easy to replace.

I see that the Lancer uses the newer metal PCV valve, so I'm not sure what can go wrong with it? Pic link...

Edit... it seems the above link is the FRAM replacement. The OEM might not be made out of metal - link Will post what the OEM is made out of when I take a look later.

Still, you guys recommend replacing it even though it is a pretty simple design?

 

If it isn't throwing a code and or running like **** I'd let her alone.
No reason to spend money unless you need to.

Save the green backs and buy some good upgrades that will also help your can run longer.
I.E. RRM light weight crank pulley.
It'll reduce ware on motor due to less spinning weight and add some ponies.

There are many things like this your can do to most any car.