Hah Gamefaqs is actually correct on that one. Basically on your first playthrough, everything maxes out at V5. Then, when you do the new game plus thing, you can upgrade them to Omega weapons for a substantial fee (that is somewhat canceled out by the bolt multiplier you can build for not getting hit). Those go up to VX (or 10) and every stat bar on the weapons will be maxed out at that point. No changes to effects though, like what happened at V5.
Personally, it's a fun waste of time, but not really worth it if you have a backlog of games (like I'm sure that you do). One playthrough will get you all the satisfaction you could want. The Skill Points are nice, but don't really effect anything in the end. One really IRRITATING thing to me was that I didn't look at the trophy requirements prior to AFTER my 2nd playthrough. I was sure I would have gotten most of them. Turns out that I had, except for one (not counting the Platinum): beat the game on hard. Now, since I figured it just had to be set to hard before starting, I went back to my final save on Playthrough 1, set it to hard, finished it, and started up playthrough 2. Whizzed through it in total on hard. No trophy. Turns out, unless you start from scratch on Hard, you don't get it. It's no big deal really, but it's just irritating to know that I have to play through AGAIN to get that. I'm sure I will someday, but still.
Oh and it's been said before but, Tools and Quest for Booty need trophies, damnit.