I've noticed the yo-yo thing pretty much every time I've bought/sold on the GTN on Pot5 (which admittedly isn't too terribly often). TRs will sell for as low at 15k at times, as high as 25k at others. Augments have sold anywhere between 50k and 125k, with a "typical" range between about 78k and 125k. There have been a few times when I've made a pretty healthy profit buying when things were ridiculously low and then waiting, but I'm usually nowhere near to being sufficiently motivated to actually watch the GTN and stick with it.
It does occur to me, though, that someone could likely make millions of credits relatively easily just by buying and selling TRs and augments, if they weren't bored to death first.
The bolded fairly describes what I've been doing and how I feel about it. You are correct, it can be tedious and boring, between gathering TRs (waiting for slicing crits and constantly checking the GTN for underpriced TRs), crafting augs, and watching the TR/aug markets to figure out what to sell and when. That said, like you, I don't have the patience to watch the entire GTN for low-priced items to sell at good profits. There is simply too much to keep track of just to figure out what's going to be profitable. By focusing on TRs and augs, I can get a pretty good handle on one small part of the market. And ultimately, it is very profitable, even when prices dip as we've seen lately.
I figure that making credits will ultimately require a commitment of some kind, and I feel like this is about as much as I'm willing to deal with. It's become habit at this point...log in, run slicing missions, check GTN, switch alts, queue crafting, rinse, repeat. I wouldn't describe it as a lot of fun, but it's effective, and ultimately not all that time-consuming.