I don't think the habitat changes in the buffalo are affecting the smallies as badly as you think. First, the river gets a TON of pressure. Much of it comes in the form of catch and keep, as the average drunk is ignorant of the restrictions. I was a lower stretch this summer and started scooping gravel with a hand net. The water was as hot as a bath, and that snot moss was growing everywhere. I still found lots of crawdads and quite a few of these other things. I think they're helgramites maybe? They look like centipedes with serious jaws. Even in the nasty hot water, I landed 30+ fish with some 16+ inchers once I switched to a baitcasting rig and my favorite topwater rig. Anyway, the forage in the buffalo is pretty abundant in my opinion.
I think stocking channel cats is a fine idea. It gives the keeping crowd something else to fish for. AGFC has stocked channels in the past and has had limited success believe it or not. There was a big study a few years back where they tagged the stocked cats, and found that quite a few had migrated all the way downstream to the white, and wound up in the delta warm-water stretches. I don't know why the cats leave the buffalo, but it probably has something to do with spawning patterns. Channels move to current and headwaters to spawn, then retreat back to reservoirs. If life is good in the river, and they can find a big still pool, they sometimes stick around. Also, while the channels share much of the same forage base as the smallies, I think they're probably more prone to scavenge and feed on larger sunfish. All in all, I don't think stocking channels will affect the smallmouth population that much, but I'm not a biologist. AGFC won't stock them if they didn't think the smallies would be okay.
Personally, I think they need new restrictions. A big slot, or C&R on all smallmouth over 12 inches might be interesting. At least that would get the message out more effectively.