I think the Sport will be the most popular trim level.
With the NB, to get stuff like the 6-speed transmission and LSD you had to step up to the LS, which brought with it a bunch of stuff like leather and Bose stereo. (The small exception here being the '99 sport, a limited-production model with 5-speed, sport suspension and LSD that was made in small quantities before the LS model was introduced for '00).
There's loads of people who want stuff like the 6-speed transmission and LSD but don't need frufru like leather seats and Bose stereo. So a Sport with Suspension package works out to a hair under 23k sticker price. The folks who want the leather seats and Bose and whatnot can still get those things, and they carry a higher price tag, but the performance features are available to the people who want a quick street car.
The one thing I think Mazda should have done but didn't, was make the Suspension package available on the Club Spec. Then you get the cheapest, lightest variant of the car with the 5-speed (which the autocrossers tend to prefer), with no AC from the factory, and it has the Bilstein shocks and LSD, and is totally eligible for stock class. Granted that'd be a limited market, but if they're offering the Club Spec at all they might as well offer it in the configuration the autocrossers really want.