Personally, I'm booking less just because the experiences have become more hit or miss for me than a couple of years ago and I have become more selective.
As far as the mention that individuals always seem to end up "fully booked", I have found that even if they are not fully booked, they are listed as such when their shift has ended, so I feel that is an inaccurate way to determine how busy things are.
And in regards to discounts, I have actually been offered a discount to book more recently, but felt that was more because the person I was booked with cancelled and because there was good feedback about me from prior bookings, so there was a desire to have me return. Ultimately I just used the discount as part of the tip, I am more concerned about my time being well spent than any discount and haven't seen discounts offered for years, was kinda surprised when it happened.
Cheers!
Le Capitaine