Relative to much larger e-Sports, such as DotA 2 or LoL, very, very low. But typically competitive games that aren't on PC fall fairly 'low' anyways. Relative to other console games, I believe it's doing fairly well. Despite what kappatards may be saying, FGC is actually beginning to see Smash as a worthy, competitive fighting game. Melee and Smash 4 are currently neck and neck for entrants to EVO with only USFIV beating them out.
Smash's real problem is that it's growth relies solely on the community whereas other games have the benefit of having a company backing it as well. DotA 2's TI5 prize pool is already pushing $11 million and that's something you'd only see with the dev's help. Warner also added $5 or $50 thousand (can't remember which) to MKX's prize pool at EVO. Aside from set ups, and tournaments that don't reflect the competitive community's interest, Nintendo hasn't really done much.
