Sounds like it would be a good idea for scenarios once in a while to have weekday frames.
Attendance in general could, I think, be boosted by more promotion than what scenarios get right now. There are a lot of AH players who don't even know what a scenario is or how fun one is and more still who have never played in even one scenario. I think the way to help is for people who like scenarios to be advocates -- to tell others what scenarios are and how great they are.
I play WWIIOL. It's a lot more realistic than, say, Battlefield 1942. But in its aspect of WWII aviation, it's not really much more realistic or involving than the AH main arena. Overall, WWIIOL (although I like it on its own) is only a pale shadow compared to the substance of a scenario.
My feeling is that scenarios and scenario participation can grow to and beyond the level of activity we had in the late 90's in Air Warrior. But it will take advocates and some cooperation from HTC.