I work so hard they don't get chance to go rusty..

Hey UB,  d'you think 2'6" is to high for a drum riser?

That depends. Are you trying to make sure your drummer can't climb up there? If so, you might want to go higher. Otherwise, 2'6" is probably okay. Any higher and someone might strain something. 

So ewe are saying the drummer may need to rise to the occasion.........or would he need to march to a different drum?

I'm saying that he may use the Bass player as a landing pad. 

I'm doing preparation for our annual bike club rally where I get to be in charge of everything in the marquee.  I decided this year we'd have a drum riser built into the stage by using longer legs for some of the stage panels.
It only makes it 1 foot higher than the rest of the stage, but the drop off the back would be 2'6"...

Not high enough?

I would go higher. One foot higher than the rest of the stage is not a lot. If you can go a bit higher without a lot of extra work or expense, that might be a good thing. If your drummer is likely to stage dive off the back of the stage, you have a different problem. When you go three feet or more above the stage, you end up adding some steps or a ladder on the back, unless watching the drummer dismount is part of the show. 

Moobs make a great cushion

Nature's bouncy castle