To really increase the userbase of the site I think you need to branch out from netplay and move into IRL Smash Scenes. I will Chronicle my suggestions in an easy to read format down below.

Multiple Rankings

Users should have multiple ratings. Netplay, Tournament Results only, and PRs (local,state,region).

Bracket Support 

If TO's were able to run a bracket in the site, and players were able to self-report matches, with dispute options available. Or a TO mode where the TO's can just report matches (no character select or stage selects required) I think you could get alot of Users. I think a TO rating system would have to be explored in-order to reduce the ability for people to troll on netplay. There will also need to be a blacklist for shitty TO's similar to Smashboards.

Smash Groups and Power Rankings of its users

Local Scenes should be able to make a group, and set geographic boundaries that auto suggest new users join the group if they fall inside said boundaries.
These local scenes should get a power ranking based on local brackets run through the site, to go along with other ratings.

Tournament Escrow Service

I think with included bracket support, and Escrow Service that provides easy prepay options. TO's would make this would the go-to site for medium-larger tournaments, the full suite of tools that are available would make it hard to justify using Challonge or Tio Pro along with their own Prepay system. The ease of use would be too tempting.

More Uses for Location information

Auto-advertise nearby tournaments, Help users carpool for a tournament, Auto-suggest local smash scenes and more things I haven't thought of yet. =P