I don't think it's worth it in dungeons, with the exception of doing CT or Turn 3 if you have i70 gear to get rid of.

Just doing FATEs in Northen Thanalan in a party is probably the fastest way to spiritbond, and you can get Alexandrite drops on top of that (assuming you're at that stage). You can get more spitibind done from one trash mob FATE than an entire dungeon run.