It might be worth checking level on other things (floor, countertop) to know which thing is the really the one that's out of whack. Perhaps could save some effort if the issue isn't the doors as you're assuming.

That said, I think that if you end up re-using the existing holes, you'll still have saggy doors and if the new hinge holes overlap the old, the sag will be even worse. A tip I found on This Old House, I think, is to put a bunch of toothpicks into the hole along with wood glue and then break off the toothpicks. It's surprisingly easy to break them off BTW. The toothpicks give the screw something to bite into. I have partial overlay doors with exposed hinges and have had success at repairs like that. The wood filler would be for holes that aren't going to be reused.

For the glides, as long as you get new versions of the same glides, it should be ok. (I know that K&V are still making the same glides as were used in my 30 yr old house!) Where it gets tricky is trying to upgrade; the locations and tolerances of the cool new glides (ball bearing, full extension, soft close etc) are far different than older 3/4 extension glides.

It's also tricky to get to the inside rear glide attachment points in smaller drawers to remove and replace. Some contortions, a flashlight that you don't have to hold, and a short screwdriver will help, or perhaps paying off a small child, if you have one available! I hope you're young enough that you don't have to wear reading glasses to boot in the process!! Oh and a pillow to cushion the cab floor edge while you're cursing, er I mean working, and the screwdriver slips for the 50th time.

Pretty please can we see some pictures when you're done?

HTH

Thank you for the reply! I'm not sure why I didn't get the email for it. :( Still kind of a noob around here!

The toothpick idea is totally genius and I will definitely be doing that!

I think we'll probably hold off on replacing the glides - it's not essential and the ones that are a little bent can probably be bent back into place without much effort. We'll try that first before replacing.

I will definitely post pictures when we're done!