Sometimes you have to. Finishing a plug weld would be no different then finishing a butt weld. If the weld is good and you don't grind down back into the base metal the strength of the repair is not the issue. I'm not understanding some of the logic presented. I could butt weld a section of taiwanese floor pan in, dress weld on both sides, make it invisible, and that's not hiding the repair, but if I put a full pan in and dress the welds on the inside it's a hack cover up. If I had to put a used inner fender in plug welded from the engine side I wouldn't just paint over the plug welds. It would need some finish work. At the end of the day it needs to resemble the side you didn't touch.