Thanks to our returned-from-the-
deadwork resident coder, azkedar, we have now fully re-enabled minecart spawning blocks as previously. Please refer to the respective page on the details. The reason why we could re-enable this is that azkedar changed our plugin that limits spawning of mobs to include vehicles. So you are allowed to have 10 minecarts per lot. Anything beyond that will trigger an alert and stop spawning the minecart.
For those who missed it: We disabled minecart spawning blocks because one could built a redstone contraption that would spawn hundreds in seconds.