Even without having read all of the above, i was thinking along similar lines as the OP.

You cannot say nice things to the NPCs without it getting into romance...and "approval" does not mean "for mating" for me. So either romance responses should be clearly distiguishable from the rest and need a "just beein nice" alternative that earns approval rating nontheless.
And maybe add some line that ends all futher romance with that NPC until you clearly state otherwise.