You only take metal off if thinning the felt, or removing it completely, makes the instrument play better but the clattering drives you or the MD or other players less than thrilled.Just be careful with this test... Having a loose part (whether that's a top cap, valve button, lyre screw, waterkey screw, etc) can introduce vibrations that change the feel of the instrument (often making it feel more open, in my experience).
I don't personally think this is a particularly reliable test - a bore camera costs £10 or so, some cocktail sticks and a ruler cost even less (both FAR less than a new valve)... I don't see that trusting subjective perceptions would be more reliable than either measurements or an eyes-on approach.
Either way, if it's worked out well for you then I'm glad that it has... I'm just not sure I'd recommend the method, myself...
Incidentally I once saw a very famous Euph player standing in front of a band which was playing the accompaniment to "Grandfather's Clock." The only audible sound was his valves clattering. He might just as well have been miming. I was only 4 rows back. it was truly pathetic!