Spirit is taking E3s. At the moment it is just renewals from other 121 carriers because it's an easier onboarding if they already have an FAA ATP.
I have not heard the rumor that they are ramping up to take fresh E3s, but it wouldn't surprise me. Things are getting shaken up here that have many looking to jump ship, who maybe 4 weeks ago saw themselves staying at Spirit for life, myself included. Spirit has many new aircraft coming this year, as well as continually announcing new destinations, so they need to keep the growth going.
You'll make more money at Spirit than at a regional and you'll get 320 time. Every airline has its issues, and Spirit has many, but I'd for sure be gunning for an LCC over a regional if you have the opportunity.