I think "wishing wells" are still done in some circles. You typically don't ask for specific gifts-- they are usually very small and unwrapped items-- pacifiers, washcloths, butt paste-- think 5.00 and less on the ticket price.
I understand the optional part of the diaper raffle, but IMO, they are not in such good taste. I know that they are becoming more and more prevalent, but that doesn't make them any less icky.
I think the wishing well is a more tactful way to go-- it's less obvious as to who participates in that. The raffle might make some people feel like they are being punished for "cheaping out" if they are not eligible for prizes. To me that's the utmost breech of etiquette-- to make your guest uncomfortable in any way.
May I suggest, if you really want to do a nice door prize, to number the bottom of each guest's plate and randomly draw maybe 3 or 4 numbers? This way everyone is included in the drawing and has the same chance of getting a prize.