I don't see the use in this. There is nothing that is a plus for having fly inside spawn. What are you going to do with the fly? It may be fun to have fly, fly around, and maybe explore a bit more.. but you can explore without fly as well. Nobody really hangs around spawn, it's for voting, being afk, a few shop signs, bank, and getting a few bars of gold. There are other reasons for spawn, but none of them require to have fly. In towny you have the ability to build so there is a big use for it. Nice idea though! :)