Every such place I know doing that (some are gem based) - quite a few in the US and Canada, share a common trait. They are in a location that attracts tourists for many reasons. They are not the main atttaction. In Chicken, the panning is so productive that when I looked it over there were 5-6 kids there panning for their summer job. They knew the mine operator well (not a hundred yards away at the time) enough to know his daily production, and if the latest scoop wasn't rich enough to justify their time, they'd have it replaced.
So, as PART of a tourist/attraction industry, it seems worthwhile - even perhaps if not self supporting as tourist dollars spent on other activities could easily justify a breakeven activity - however, panning as the main tourist attraction off the beaten path seems unlikely to succeed.