It's a good idea. I proposed something similar (limiting the number of traits a girl could have) a year or so back. Unfortunately one our more outspoken modders took exception to the notion that his creative impulses should be subject to interference from a mere developer and the idea was dropped.
We could put a points system into WMEdit, but that on its own wouldn't be enough, since you could get around the restrictions by directly editing the XML files. We could put a points checker into the game, but that breaks a lot of existing girls, which is unlikely to be a welcome development.
There was one thing I did consider at the time, but never got around to doing, and that was doing "lite" versions of existing girlpacks. The pictures are already collected; all it needs is for someone to produce a balanced girlsx file for them
Which admittedly, would probably be easier with a points based WMEdit app... Hmm.
I don't think that it would matter if some one edited the XML files. If they wanted to do it, they could do it for their own enjoyment, but it stops most players from having an easy, run of the mill game experience every time they played it. Some one would have to go out of the way to edit their girls and make them stronger, in which case they would probably find another loophole anyway. If some one were to post the girls packets, it should be mentioned that they're over powered, as it probably should mention already.
The point would be more to normalize girls, anyway. To give an "Average", to some extent, which makes it slightly more challenging. I think having a restriction on traits would be a good idea, at least initially. Perhaps even an option to help a girl develop certain traits with certain forms of training. As Whore Master is now, that would be a bit tedious, but if the amount of girls was scaled down a bit, I think that would be great.
I still think that it should be scaled down. Instead of 25 girls making up a full brothel, maybe 7 should be full. Every girl makes more money, and getting new girls is a bit more of a mile stone. Maybe even different forms of jobs, too, which could be unrelated to the brothel, and they could work in town to do these things... Such as a fighting instructor at a dojo, or a secretary at an office. This would train them in certain skills while still giving some money.
Back to the original point though, I think that would be a great idea to have them done by skill, and each level up would give them another amount of stats, say between 50-75 distributed semi-randomly with a 50% chance of acquiring a new trait. Traits could be ranked on different tiers, with stuff like small boobs and lolita as the first tier, up to things like incorporeal as the third tier, that way a girl doesn't randomly turn into a construct when she levels up... Maybe there could be a fourth tier for things like non-human, which she would not level up in to.
I don't know how most of this would work out for a programmer, just kinda throwing out ideas I suppose.