Theme song doesn't change, but the VA of Star admitted her voice acting in the earliest episodes, if that's what you watched, was kinda rough and got better over time.
I think it gets better toward the middle/end of the first season when more of a plot shows up and is pretty consistently good in the second. Think the plot got retarded by the third season, but some people like it and there's another season left in which things could possibly get better.
Maybe try watching a few random episodes from later in the series or even check out a season finale just to see if any of the plot might interest you. If neither the plot or humor draw you in or you just stay annoyed with it, it's pretty safe to assume you won't be missing much if you just stick with the porn.