Does anybody use an under the saddle bag for touring? (Not Pannier Bags) I am looking for a bag as an addition to my backpack to use for cycling. A pannier isn't a choice I want to make, because I believe they balance the weight badly, and that there is some risk of broken spokes on the rear wheel when using a pannier. 

I started looking for other options and finally found this one:

Bag details:
Volume: 7 liters (1.85 US gal)
Weight: 250 g. (8.8 oz)
Material: “Titan”
Material density: 1680D
Basic colors: black or gray
Additional colors: orange, blue, yellow, red, green, light green, lime color.
Price: $59
I have seen similar setups for MTB touring that use a large seatpack, a frame pack and a handlebar pack to get enough capacity. This setup also allows a better weight balance.

Bikepacking.net

is a good site for getting ideas for different setups. This site might also give you some ideas as well. I know we aren't supposed to recommend gear, but I've been very happy with the stuff I have got from Revelate Designs. 

Revelate Designs

IMHO, your concerns about panniers are unfounded if you plan to tour on anything like a road. Panniers can be a problem if you are touring on trails or your bike geometry doesn't provide sufficient heel clearance ( often a problem on MTB bikes)