Stick with your best idea and develop the map. Try perfecting it till its a quality scenario. I have had many ideas for multiplayer rpgs since I started such as X-Men, Camelot, and others which are just out of my mind. But I stuck with the same old Chris rpg demo (my first map) and now it has evolved a great deal. When I started the map, I did not even know how to use triggers, but gradually learned.
It does become boring. This map was started back in December and still going, although I hardly work on it due to boredom...I havent touched it in over a month and a half...but today I worked on it a great deal. I am seeing more multiplayer posts here and got some motivation to continue. In conclusion, I suggest sticking with one map at a time.