It's nice to hear the words "Thank you." That's all we need. But it's even more important to hear about where we are going wrong. And yes, people do offer tips and I think most are politely refused, as they should be. Unlike many service industry staff, we are appropriately paid for what we do.
As for working in the premium areas of the cabin, that normally given to the more experienced crew members. These passengers pay more and every attempt is made to give them more.
PM