I never thought of the Tanners as "wealthy". Two quotes come to mind here. There's Danny's quote from The House Meets The Mouse Part 1 where Danny says Kimmy can't go to Disneyworld with them because the Tanner family budget is already a little streteched (or something to that effect). Then in Comet's Excellent Adventure, when DJ says she's breaking up with Nelson, Stephanie says "Well, I guess it's back to rubbing elbows with poor people".
Besides, I don't consider $90-12,000 a year to be "wealthy". It's certainly not poor, but it's not wealthy either. Do you have any idea how much some CEOs make these days? There are CEOS who make that much money in one day. Those are the wealthy people in this society, and their level of wealth is truly obscene. These are people who have more money than they know what to do with. We could solve homelessness and world hunger with the money that truly wealthy people can't manage to spend.