You said "Dumb idea, anyway, a twin-engined jet loitering around at 1,500 feet"
What do you think S-3's did for decades? As a former pilot of both platforms, I will tell you that the Viking was way better at ASW than the Orion. Yeah - I could tell that when we would pass a contact off to an S3, go off station, they would loose it, we would come back the next day, find it, track it, turn it over, they would loose it... THREE TIMES!
... the airframe itself is aerodynamically unstable, making it a bear to fly (even with the not-so-reliable auto pilot.) Gee, I didn't think it was such a bear - pretty good handling, especially if light. And the auto pilot worked fine if you had a good IFT on board.
Finally, given new technologies, there's no reason for future aircraft to have to fly that low to perform effective ASW. If you want your sonobouy pattern to look like it was layed down with shotgun... and MAD technology hasn't done much beter - still gotta be close enough to the bad guy. So even if you want to decend to lay a pattern, climb to save gas (but you'll be there for such a relatively short time you won't recover the fuel you burn to get there), repeat for X times or until the bouys run out (oh yeah... how many bouys can the S3 carry?) and finally decend for the MAD run - times X depending on water conditions, your sensor operator and equipment calibration.
The ASW and MAP mission is all about options, as you know. A bus can carry more options than the bug.
There may be a better platform out there, but it ain't the one from this thread (IMHO).