If you go with the power wire-wheel, use a light touch, and keep it moving.
Those things can generate a surprising amount of heat in the work-piece, and there's a chance of warping that stamped platter.
Suggest scraping the majority off with a razor-blade scraper, then removing the rest with wire-wheel, or sanding.
The home centers used to sell an adhesive solvent for mastic and similar tile / linoleum / cove-base applications. It would be found with the paint-thinners and strippers. You might check into that.
The factory would have used a glue that was cheap, set quickly, and would not soak-into the felt.
My first guesses would have been hide-glue or shellac. Varnish takes a long time to dry, so that would not be at the top of my list.
Hide glue melts around 140-150* F, you might try placing the platter in a 150* F oven (use a reliable oven thermometer) for a half-hour or so, and see if that softens the glue, if so, heavily dampen some paper-towels and lay those over the top, and leave in oven for another 15 minutes, and see if that softens the glue enough to remove.
You shouldn't need to worry about excavating the glue from the channels, only the high-spots.
Good luck !
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