Love the tag manager idea. Here's some feedback.

This tool is screaming for column sort, checkbox, and a merge or delete button.

Some example tags for me:

Lexus LC500
Lexus LC500 C
Lexus LC500-C
Lexus LC500C
LC500

The ability to put a check box next to those and click "Merge", then select which one to merge into, would be the ideal from a UX standpoint. Being able to sort and filter tags would be an essential part of this tool. The same goes for being able to multi-select junk tags and delete.

I understand it might need to be a different page from the existing interface.

100% agree. The Tag feature is very limited and needs to include merging and sorting/filtering. This would be the most crucial add-on or feature upgrade.