Should I leave faced fiberglass in my basement energy walls or replace it with rigid foam?
You'll get a lot of opinions on this subject, and there are several lengthy discussions to be found on SE, but the bottom line is that each case needs to be handled individually. 

In my area, it's common to have framed energy walls with unfaced fiberglass batts (not faced like you have). Sometimes moisture is an issue, so it's commonly advised to forego a moisture barrier inside the insulation so that the wall can breath and dry out. You don't tend to get the type of condensation that you would in a main-floor wall, which is exposed to the outside air. Poly sheeting is often installed over the insulation in unfinished basements to protect and contain the insulation, and it may or may not be removed when the walls are finished. 

In your case, if it hasn't been a problem to date, it probably won't be in the future.