I'd think echoing would actually make determining where someone is much harder. And, in Dvergeheim and below where everything is falling and shaking all the time, creatures based solely on hearing should be at a disadvatage.
But, yeah, back to sneak gear...
I have determined that it's just not bloody dropping. Anywhere. Ever. Shadowed hoods, soft leather boots, lesser and normal mantles of the forest walker... they're all you can expect from any loot drops, anywhere.
Spot gear is also pretty low. I found a Hector's Bangle today, after not seeing one in many months, and didn't even recognize it. Thought it was a sparkling band for a moment.
In demonologists, the monks there have a higher percentage of having some monk gear on them (almost all of them have something... most is vendor trash, white gis, holy virgin robes, garbs of mankind... but at least once on every max spawn run we get a pair of "better" gloves like iron hands, or green dragons, and once in a blue moon we even rolled a red gi off one of the monks). Maybe the same should be true for some of the heavy hitting sneaks in various places. Assassins and such in the Forest Fane are pretty tough. Maybe some random chances for loot drops for them w/ some sneak gear. Maybe chances of sneak and spot/search gears for the lookouts. You'd need to scale it to make sure they weren't always dropping something, but once in a while would make sense. There are also some sneak and weaponmaster types in the bandit house in Demeuntlieu, so that would make sense there too.