there's a thread on here that gives some examples, but yes i believe it does scale with herb level. with non-rested xp, i was get around 1200xp per saronite (425 skill level) on a 73 warlock, yet i was getting 2200xp per goldclover (450 skill level)
oh yeah, i got 1.5 levels (72 now 73.5) on my lock just flying around gathering. It's slow but not horribly so, considering I was asleep. Not to mention the several thousand G earned doing so....