The "power groove" idea sounds plausible, but I have two problems with it. First, I'd have to be shown before and after performance figures proving that it actually works. It seems to me that it could also cause additional turbulence that could obstruct the flow of the intake gases. Unfortunately, I no longer have a picture of them, but I can still see the those valves from that Mini Cooper that were actually ground down to a much thinner cross-section and polished to a mirror surface. That engine vaporized so much fuel that we'd get ice crystals forming on the outside of the intake manifold after a couple of hot practice laps.
Second, how much return do you get for how much cost? After a while, you reach a point of diminishing returns. In other words, it costs more and more for increasingly smaller incremental improvements.