High-level people don't want to play through low level dungeons cause they are boring, partly because they are crippled in skills.
Roulette bonus was made specifically to incentivize people doing the low level dungeons as necessary despite them not wanting to due to how boring they are.
You want to remove the boring aspect of them, and make them more fun than the high level content...cause let's be honest, sometimes it's actually fun to "melt" the large groups like they were nothing.

Solution?! Remove the roulette bonus altogether...Sure, go ahead and guess how many people will actually DO it then?!

You want to be "rewarded" for being rewarded. And you want that while hurting new players, which WILL get kicked more often with this change. No matter how much you say they won't. Then there are people that will just leave or provoke being kicked cause they got a higher level dungeon that would take twice as long as if they got a low level one. Tanks and healers could afford doing that, seeing as their queue is almost instant, getting a chance at an even faster run.

You really don't know how "people" work. Heck, you don't even seem to understand what motivates you. Just thinking that it would be "cool", without actually thinking (or outright denying when told of them) about the consequences won't help anyone with anything.