Hey there,
I have only one experience with selling things at a swap, and it was a good experience. i am not sure about the higher price opinion, my take on it is just that it is a higher likelihood of actually selling something, which equates to more money.
i had a raleigh 3-spd that i found for $25, put about 25 more in cleaning and new brakes, turned around and sold it at a swap for $125. mind you, this was in fairbanks alaska where a raleigh 3-spd is basically useless most of the year. when i went to pick thru the scraps towards the end of the swap there were basically no bikes left- all had been purchased. Not much gear left either, so again my take is that you just have a higher chance of selling something, not necessarily getting more money from it.
just my opinion, good luck!