My thought would be this: If you are using some good quality cloth and resin (say biaxial cloth and epoxy), then likely whatever layup schedule you use will be stronger than original. I'd lay in maybe three layers of biax and see how the level is, and then if it's at all close use fairing compound to make it just right. Obviously you don't want a thick layer of fairing compound though. If you're a bit low after the biax, you could add something like a layer of 10 oz "regular" cloth. Will be easier to fair and take up some space too. If you're really low, then another layer of the biax.
Sometimes I let it cure and then sand and fair (and sand more); other times I lay on the fairing compound while the "real" layup is in the green stage, then only have to sand once. Peel ply is good stuff. I've never used it for a repair where I was "making thickness" though (have always done layup, faired a bit proud, then sanded flat). Okay, now I'm scratching my head to remember where I DID use it? I guess it must have been on something where it was a layer of glass over a firm sub-surface vs. a build-it-up layup. Like say I was glassing over some wood with 10 oz cloth and then Peel ply on top for an easy nice finish.
I think I'd figure I'd never get the level just right using the Peel Ply and so would have to fair and sand anyway, so kind of "wasting" the Peel Ply.
But then too, I can't remember exactly what the area looks like that you are re-glassing here. And maybe you're better than I am at making it come out just right without fairing/sanding.
