The bonus + normal reward for whatever content you land on makes sense. It's scaled so you get a reward that is fair to the difficulty of the content you're doing (no matter how trivial the difference in difficulty between the dungeons is to you personally).
Also, I like the idea of losing the bonus if you quit. I thought this is how it should have worked all along. If you're playing roulette in a casino, you don't get a mulligan if you don't like the number the ball lands on. You should have to take what you get, or throw away the bonus if you feel that strongly about not even attempting the content, or quitting early on people that need the clear/exp (i.e. the reason this feature was implemented in the first place). Maybe you should get another shot at the bonus if you stick around for 30 minutes or x amount of deaths to show you're at least giving it an honest attempt, but no question you should lose it if you don't even try because you don't like the dungeon you got.
On a related note, as others have said: Not getting penalized for quitting while someone is still in a cut-scene is just bad.I also agree that 30 minutes is not enough. Maybe an hour twiddling your thumbs will give you an idea of what the DPS you just bailed on have to go through because of you, and make you think twice before you do it again.(see my post below) This lockout should also apply to queing with groups in party finder as well, just for good measure.
