I have the same situation, and here's a partial method:
In a view that shows all the various copies of the file (such as a view sorted by Name/title), I select all of the tracks I want to tag the same way. Then I open the Tag dialog and set all the desired tag values. They will be applied to ALL the selected files.
Then, if a particular file needs a bit different tag, I change it as necessary.
This technique can even be used if the files are already partially tagged. Select ALL the files to tag, the open the Tag dialog. When a tag already has a value, MC will show "Varies". If the desire is to make them all the same, type in the desired value. However, this is also a caution: If the desire is to NOT make this particular tag the same, don't touch it, tag the individual files later.
The downside of this is that it requires retyping the field, unless I first select one file and copy the value, then select all the others. That's usually not worth the trouble.
MC's multi-file tagging is particularly helpful with Keyword and other multi-value/List tags. If the tag has different List values among the selected files, it will say Varies. Click to see the actual values. It will show all the values that are selected in at least one of the files. To set that tag to the same List of values for all the selected files, just check/uncheck them as desired.
This method usually gets me 80%-90% of the way. Then for tracks that must have somewhat different tags, I either retype a tag, or if the difference copy+paste the tag then revise. For instance, for a view that groups by Name (or whatever) it's important that the value is exactly the same in each file, including capitalization. One quick solution is to copy+paste the correct value into all the selected tracks.
Two side-notes:
Identifying different versions of same-Name/Artist files: I often retain multiple files that are essentially identical, at least at the tag level, because they are actually slightly different, such as the many different versions of certain Beatles songs (the newest CD release in some cases provides 3 or 4 versions of the same song). I like the song title (Name tag) to be accurate and identical for all different recordings of a song. So, to identify different recordings/mixes/whatever, I use a custom field RecVer (Recording Version). I make sure it is different for each track that has the same Name.
Then, I want to be sure all my files have unique names, so I won't inadvertently overwrite any should they need to be put in the same folder for some reason. The RecVer field makes this possible. For all my files, I use a complex Rename expression that creates the file name by combining Name and RecVer (if not empty) and Artists (another custom field, different discussion), but limiting some lengths to be legit file names, then forcing the whole thing to lowercase to be OS-agnostic.