Going for broke by running a presidential candidate is a surefire way to lose, and no one really donates to parties that lose. Which is a problem, because presidential campaigns cost a crapton of money; Bernie 2016 cost $220M and that was the primary.
If you look at successful third or fourth parties in FPTP nations, they are generally running lots of local campaigns, which are cheaper, give a place to train a talent pool, and also show voters proof that they can get a job done. I don’t think I’ve ever seen a formal third party running for local positions near me. And in this role they can serve as kingmaker; they may never get the top job, but in a perenially razor-thin Senate margin and a currently thin House margin they could certainly lord a lot of power even with a handful of seats.