I've been doing Endurance because it's cheap, not gonna lie. And to be honest, I stay away from the sprints except when I get an occasional urge to run them just because the "race counter" starts all over if I sign up for one, meaning it's a crapload of money for 7 laps when I just paid $80 for an hour of racing straight through and morning practice.

I don't know the solution so I won't claim to have one, but if lets say two endurance races was $100 and adding some sprint racing (which is really just 7 laps at that point, nothing more) was reasonably priced, I'd run sprints too. As it stands now the cost penalty for a mainly-endurance racer running sprint as well is just kinda steep.