Not worth it. There are over 30 mods, (suffixes and prefixes, not to mention those that can get BOTH). Not only that, those mods emcompass many numbers per percentage, which makes it 5*30^3. You need 3 PGems per each reroll, and having forty of them is 13 rolls. There's a small chance for you to get a GC with +skills. And by small, I mean miniscule. It's like Vegas: you don't reroll when you're feeling lucky, you reroll when you're feeling really lucky. 40 PGems is a high rune, sometimes you can offer less, depending on the person who wants them.
xD