Tinkers are actually a pretty solid class - certainly not broken like Transmuters, but I'd probably rate them in the same tier as Rogues and Paladins. Even on a purist run, it's rare that I'm unable to buy just about everything I'd want to - either thanks to a treasure subdungeon, Tikki Tooki, Midas Gloves, or stealing then transmuting something expensive like the Orb of Zot. Like his alpha incarnation, of course, how powerful he is depends on what items are available - and dungeons where every other shop is selling something nearly useless, like a Burn Salve, are frustratingly common.
(A suggestion: if Fortitude Tonics and Burn Salves are not going to be changed in any other way, at least give them a higher conversion value. I'll still buy a Troll Heart even though its primary use is worthless, just for the conversion points; I virtually never buy either of those potions, though, because they're just so ridiculously niche and quite weak even at that, and have no worth outside of that niche.)