It is why I tend to skip versions of the program...too much bother buying and loading a new one when many of its upgrades only apply to files I do not use...
You should never have to re-import anything, or start over from scratch, or remove anything from your existing library, when you upgrade to a new version of MC.
If the installation of the new version of MC doesn't find your old library, and use that as it is, then the best advice is to back up the old library before upgrading, and then restore that backup into the new version, with all settings, as mentioned here:
You can backup your library so it keeps all your settings. Along with setting it to search only specific folders vs looking all over your computer as you have experienced.
Also as Jim suggests, if your existing library is looking everywhere for all sorts of files, you need to check your Auto Import settings. MC certainly shouldn't be looking all over your network for all file types!