Most of the towns in those 'second-tier provinces' look the same to me. Okay, there is one, or the other national park, waterfall, or 'different' temple, but for individual travellers, going there is too troublesome (not to mention the highly inflated prices for foreign tourists in regards to sights, local transportation, etc.)
And I doubt that Chinese bus tourists would enjoy such long journeys. When I travel to/in Thailand, I want to see beaches, not recently built Wats in Nakhon Nowhere, 500km inland...