Interesting issue this one, and I was discussing this just the other day with a potential "retro-tradder"
I think if the route is an established sport route, it would be quite pointless to headpoint the funk out of it, solo/lead on trad gear and chop the bolts. You could potentially de-gear alot of good mid-grade sport around the country like this! Clearly some routes will make decent trad routes and I think this could be an interesting approach, on a route for route basis.
(The two routes given as examples above, Supercrack and Rattle Those Tusks, are slightly different in that they follow strong crack lines and were originally trad routes. There is a very strong case to remove the bolts on these. That's another debate.)
If you are going to lead something on marginal gear / big fall potential then you definitely want to remove the temptation to just clip a bolt. The problem with taping hangars is that it is still pretty easy to ram a quick draw through them if you get gripped. You could remove the hangars but it would still be possible to loop a wire over and lower off, or grab it and ask for rescue.
I recently made a prototype steel plate 'bolt-blocker' that clamps over a plate hangar, tightened with just a small adjustable spanner - no chance of clipping or even grabbing a bolt with one of these on. I'm going to try and get some more made when I have the time. Tom, if you send me a photo of the hangars in question I can make some specifically for you.
Mark