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@lae
Toothpaste is a mild abrasive, but I don't think it'll work. Bearings become pitted because the outside surface of the bearing is harder than the inner metal (this is called case-hardening). If bearings are over-tightened or aren't maintained, the ball-bearings weld themselves (microscopically!) to the bearing surface, which rips off little flakes of metal each time the bearing rotates. This exposes the softer inner material, which wears much much much faster than the hardened outer layer, leading to visible pits in the surface. Abrading the bearing surfaces further will only exacerbate the problem!
Old Campagnolo Record bearings are hardened all the way through, which is why they last forever.
A slightly worn bearing is okay to use, IME. It'll need more frequent maintenance than a good bearing, but if it's greased and adjusted correctly, I think any increase in bearing resistance would be so slight that you probably wouldn't notice it. I suppose it's possible for a bearing to become so worn as to collapse (which could potentially cause significant wheel-wobble, or even break an axle) but I've never seen it happen.