There's a winery there but Thai wines are usually terrible. If you don't know anything about it why do you want to visit?
Doi Tung is worth a visit if passing by but I wouldn't go out of my way for that area. I found it a bit dull. The area south to Phayao has better scenary and Wat Ananlayo is good.
Mae Chan doesn't seem to have attractions that can stand on thier own which would compel people to make it a destination. I see it more as a town that we pass by on the way from Chiang Rai to Mae Sai, or as a turning point to Mae Salong from Chiang Rai. There's not much info on Mae Chan because areas surrounding it are more attractive. If anyone has nice stuffs to share about this area, would love to hear.
It's a totally nowhere town next to the highway in between Chiang Rai and Mae Sai. If you want to spend some extra time in between Chiang Rai and Chiang Khong I would go to Chiang Saen. Much more to see and do there. Otherwise go up into the hills at Doi Tung or Mae Salong.