I think that the WordPress theme market has matured to the point that there is healthy competition, with a few companies/sites rising to the top (ThemeForest, StudioPress, Elegant Themes, etc.)

As a WordPress theme affiliate now for a half-dozen years I still believe there is plenty of room for new entrants – but serving a niche or developing your themes in a way that stands out from the competition is what will (in my opinion) bring you the most success:
Elegant Themes – complete access to 80+ themes for $69
StudioPress – the Genesis Framework
ThemeForest – the largest selection of themes
Hermes Themes – built specifically for the hotel industry
Additionally, I believe that many companies don’t do very well (if at all) when testing their conversion rates and pricing strategies.