I love those bass drum cymbal mounts. Most of the drums that I have came with them but if they didn't , I usually put one on, when I find an original. A lot of them doubled as FT leg mounts,so they are easier to find than one would think. Regarding the issue of devaluing. It sounds like your drum has already had its share of that anyway and if you use one of the o.e. items being offered to you , it's value will probably increase----especially if you have an original arm to go with it. An untouched original drum in fine shape would be a whole other matter , though.
The real issue with drilling new holes in a shell, is to do with non-original replacement parts and the fitting of odd accessories in wierd places. Putting an original equipment part in its correct place is generally a good idea.
-----a little historical aside. In 1967, I ordered a brand new Trixon W.M.P.,16X16 floor tom from a music shop in North Toronto. The distributor,was Efkay music in Montreal and the drum arrived in about a week. Unknown to me when I ordered, Trixon had discontinued, mufflers as standard equipment, so I asked the shop to put a muffler in it. I returned in 3 or 4 days to pick it up and it had a nice new shiny------------------------------------------------------------------------------------------------------------------------------------------------------------------------Rogers muffler in it! How thoughtfull of them.