ok sounds ingenius but will reimporting be significantly quicker than tag updates?
I don't know, it depends on how fast your system and drives are, file formats
*, file fragmentation, etc.
However, I am sure that creating new backup files of 560 files (= 2%) is much faster than creating new backup files of 28000 files. (Personally I use a backup program that can update only the changed files on my external hard drives in which I keep two separate backups sets.) The same is true if you sync portables.
Also, you may find an explanation for the missing tags (in case you don't already know).
Edit
* Actually, the used tagging format is the key factor. If the files contain appropriate padding area for new tags then the tag update is quite fast. If not, then a complete rewrite is needed. In the latter case importing is certainly faster.