In this thread a few folks have bashed "dino" oils, but in fact, it appears that in dirtying themselves in just a few hundred miles, they're doing exactly what they're supposed to do -- clean the engine. I don't believe the cheap cleaners/flushes (Rislone, CD2, Marvel Mystery, Valvoline 5 minute flush, etc.) are useless, in spite of their simplistic formulations (kerosene, mineral oil, naphtha, etc.). But using anything resembling a "shock" treatment may be dangerous if your engine is as cruded-up as you suggest -- you could potentially dislodge stuff which could cause you circulation problems. So a slower approach might be appropriate, such as AutoRX, "diesel" motor oil, etc. Or if your current method is working well, what the heck, stick with it, especially if you're using 69 cent after-rebate oil. Make sure to regularly change your filter through this process as well.
As for pouring a quart of oil through the engine at the end of an oil change, that would certainly be a waste for several reasons, but notably, the oil would drain only through the oil channels directly below the oil cap, leaving most of the oil system untouched (not that this would accomplish anything anyway).