if you want consistent XP and progress, queue for the dungeon you want, or select a few you like and leave it up to chance. If you want the bonus and maybe helping someone out? Pray to RNG-sus and DF it up.
I don't think this system need to be more complex. It serves it's purpose: helping new people complete old content. I understand you're all past it.. but just because you don't want black 2 coming up on the roulette wheel, doesn't mean you aren't going to get it.