Final Fantasy and a Star wars game, both of which enjoy magazine space your average thousand arms or hoshigami could only dream of, are hardly indicative that Atlus RPG titles are becoming mainstream.
You can't really be arguing that Atlus SRPGs aren't niche? Just look at Atlus's entire PSone/2 back catalogue sales/ print run figures. Maybe I just misread your tone.
As far as I can tell, Atlus seem to have an excruciatingly small localisation team in America with one small yet thoroughly personable PR lady there and that's it. Despite the fact they've been going all these years they don't seem to care about investing in Europe.
Disgaea really should be hunted down by all people who love quality games though. It's my favourite game from last year and one that could seriously keep you going for years and years. I completed FF Tactics twice and there's nothing extra for the replay really. Disgaea is a title I keep dipping into and intend to for a very long time to come.