Hi again, Lynn!
This is going to sound snide as all get-out, but aqua aerobics is not exactly a hotbed of high-intensity instructors. I've seen that even if the instructor is in good physical condition, the class that the instructor leads is very low-intensity and IMHO not very effective for cardiovascular or muscle conditioning unless it's for a very beginning participant for whom any training stimulus is new.
If you don't feel like you're getting a good workout in the water, it's usually because you're . . . well, not getting a good workout. I tend to go on the high end, with a lot of faster-paced running drills, long-lever kicking drills to the front and back, power jumps with the legs in various positions, and upper body stuff while keeping the legs busy in a jack or ski move. And I like to do a lot of deep-water stuff with styrofoam hand buoys as floats.
My suggestion is: give the classes you're considering a couple of tries, and if it doesn't get you where you want, just switch over to a swimming protocol, alternating total-body swimming strokes like crawl and breaststroke with kickboard flutter-kick, dolphin-kick and frog (or "whip") kick drills so that the legs are recruited more. Also consider investing in an Aqua Jogger float belt, and do aqua-jogging running drills in the deep end.
Lemme know how things work out. You have my sympathies in that kiln known as Arizona. Stay cool!
A-jock.