Wow. You are all much, much nicer people than I am....
Turns out our vacation this fall coincided with when friends of ours were heading down to California (we booked a 1 bedroom at VGC for 4 nights before they arrive). What we offered them was this:
We'd get a 2 bedroom lock-off for the nights they are at Disney, so there will be plenty of bathrooms and beds for our daughters, and what it would cost them would be $850 ($10/pt x 85 points - which is the number of points that 5 nights in a studio would have cost them).
They get all the luxuries of staying at the VGC including laundry, full kitchen (to save on meals) and everything else, and it costs them $170 night (all-in).
We get our dues/taxes for the year pretty much covered (200 pt contract) and they get to stay for less than 1/2 (parking, sales tax, etc) what they budgeted to pay to stay on site.
Judging by everyone else's responses, I guess I should feel bad about asking for money, but I think I'm being fair, and they think it's more than fair (they keep telling us they don't think they are paying enough), so I think I'm ok with it.
Putting my lawyer hat on, I guess that maybe the difference with my situation is that our friends were going anyway, as opposed to inviting friends to come down with us. If I invited someone to come to Disney, I would hope that they would offer to pay something, but I wouldn't ask them to.
Am I a horrible person????? I need to know, and who better to tell me than anonymous people on a message board...