Just because they’re paid above minimum wage doesn’t mean you can’t give them more. I’ve always liked tipping, it means they work for me too. Especially if you go to someplace regularly, if you get a reputation as a good tipper they work harder for you. Got a co-worker that brings in donuts every Friday, goes to the same place for them every week, and he tips, they start assembling his donut order the minute the see his car pull into the parking lot, even if the place is packed he’s in and out in no time. Even behind the counter folks can do a better job for people they like, and since it is a job and they’re there to make money there’s a very easy way to make them like you.
In general I wouldn’t tip for counter service, but will definitely tip if it means better future service like you describe if I’m a regular, at the table or behind the counter.
I can see doing that if you are at the same place every morning if you get your supersized double-whipped, extra frothy, honey-sweetened double mocha espresso latte frappucino something-or-other with extra cinnamon and a shot of caramel. Coffee black, not so much.