The big jump used to be after the first year. But there's a bidding war on for new-hires right now...

Most of the regionals have raised new-hire pay from 20K to 30K+ plus (hourly rate, bonuses, or some combination). Some regionals pay high-30's second year and then FO pay typically stagnates around 40K. At some airlines, you could get to 50K by aggressive schedule manipulation (may require some seniority in base).

A few regionals get into the mid/hi-40's based on hourly rate alone within a couple years.

As to whether the 121 time will help...don't let it interfere with acquiring military PIC in a tactical aircraft. But it is another box to check so you might consider it if you get 1000+ mil PIC and don't get called.

Regional time doesn't seem to be an instant cure for mil dudes who have weak resumes (or "issues") to begin with but we are seeing a lot of mil "pack" guys getting hired out of regionals during their first year or two. Maybe some of those would have gotten hired anyway, but maybe not.

I imagine the regionals are important for ex-AD guys who don't have a reserve flying gig.