It would look good, but I am not sure the laquer would stick well to a polished surface.
True... though I have seen some gorgeous MTBs that have been polished then lacquered on retrobike. If I could be bothered I'd do the same to my 90s Marin Mount Vision look-alike, but it's a bit of a faff.
Maybe marine epoxy paint would, but that requires judicious use of a mask, or preferably a respirator.
Interesting thoughts. I hear that you can get aluminium anodied in a clear coat to maintain a seal between the environment and metal. My gear stick in my car is treated in this way. Might be a step too far for a cheap old bike frame like mine though.