Yeah I would love to do me some spacebuild! I hope they add a similar system for mods on dedicated servers (otherwise I guess porting over my addons folder from gmod could work, but take awhile lol).
Well in the Gmod 13 beta almost all mods are available through the Steam Workshop. They can even be downloaded while you play. It's really convenient and easy. If you're missing something from a server you can just download it on the workshop while the game is still running