I'm going to play a bit of the devils advocate here, . When one, "does up a blade," there are many things to be factored in. First the cost. Second preference of taste. third, for what reason. I have known some swords done up by people who were not happy how they looked when obtained. The money, the time and the effort put in may be quite substantial. An old sword, taken from a gunto and put into Samurai mounts, more often than enough, ends up with money lost. Most who do up a sword do so with good intentions of keeping the sword for life. However, one never knows what is around the corner. If for some reason, this done up sword must now be sold, chances are, the money spent and not including the effort, will not be repaid.
Most serious collectors, are able to tell, a sword that has been done up. The main thing, the serious collector is interested in is the blade. I bet quite a few here, have seen a good blade done up, has liked the blade, but not the fittings? Whether one does not agree with this point or not, how many have sold a blade in shira saya and been asked, where is the koshirae? The original Koshirae (unless ruined) even gunto, constitutes a package. Whether one likes it or not, most I believe, would prefer the package. The price difference between a sword in a shirasaya and package, can be quite dramatic.
I am looking at this from a monetary view. Whether one doesn't want to be mercenary, at the end of the day, it's still money.