The guides I know (quite a few) find that guiding clients and teaching classes is so different from being out there having fun, that at the end of the week they are raring to go climbing for themselves. No problem burning out there.
If you want to make a good living at it, it seems that you have to approach it as a business. You wanna be a guiding company, not a guide, if you want to live better than cheque to cheque.
It's hard on the body too. You might not be out there pulling down on 5.11 every day (although it can happen), but there are other overuse injuries that are common amongst the guides I know. Say goodbye to you elbows if you do much multi pitch work. Pulling two ropes all day seems to kill them pretty quick.
Check out the ACMG website too (www.acmg.ca). They have also a certification program similar to the AMGA.
Most full mountain guides say that is similar too getting a university degree in terms of time and money.
Good Luck.