You know, I like this thought about not just Qing once a day to get the bonus.
To add to my thoughts about two tier rewards let's also ramp up the reward and spread if across multiple dungeon runs. I'd suggest rewarding up to 5 times in each roulette category taking the current reward as the baseline, I think you could scale it as follows (starting from a baseline of 10000gil);
2000 (20%) on the 1st run, 4000 (40%) for the 2nd and 8000 (80%) from the 3rd, then 4000 (40%) for the 4th, 2000 (20%) for the 5th and no additional bonus beyond that.
So a player that puts in the time for 5 runs, is awarded a cumulative bonus 20000gil, rather than the 10000gil from the baseline. The reward is larger overall, but you have to put in more effort to obtain it.
Combined with a two tier system such as the one I suggested, if a tank and healer Q through roulette together, the tank might get that full 20000gil, but the healer would net 16000gil (1600 + 3200 + 6400 + 3200 + 1600 = 16000) rewarding them for their time as well.
This would work for each category of Roulette separately. So a dedicated player would earn considerable bonuses over the course of a day, but would have to run something like 25 instances of one kind or another through DF to obtain the full rewards.
I think this will also not encourage non tanks/healers from Qing just for the bonus and fast Q since they have to invest more time to obtain the full bonus.