"Nowheresville" is extremely american.
just FYI. and 'small community dwelling' isn't as nice sounding as 'small community nestled' ... but you don't really 'nest' on a plateau methinks (it's fine for smaller enclosed/sheltered regions, which plateaus don't really fit...).
the question of a 'sparely' populated region really depends on the sort of community it is, if you're talking a town/urban area then sparsely doesn't fit very well.
otherwise, if you're referring to a rural-farming or hunter-gather style (nomadic) community then it would be sparse... "scattered" is also good.
"small", "minor", or "self-reliant" (kinda implying small, isolated but a positive connotation).
"obscure" is also nice, with "inconspicuous", "lonesome", "remote", "secluded", or "unsung"...
"tributary" is a great word, but may not be what you're aiming for.
and "Vibrant" is a nice word if you want to use a second adjective to counter the negative connotations of being small...
my 2 cent.