[MCBastos]

OK, I just noticed an odd bug with the way Generate Cover processes the data fields:
If there's an "&" character, it treats it as if it were " & " -- that is, it inserts spaces before and after the "&" character.
Which results in ugly extra spaces whenever it runs into an "&" -- like, say, for a book with two authors.
Partial workaround: manually edit the text in the "content" tab so "&" is not surrounded by spaces -- that reduces the double space to single spaces. AFAIK, however, there is no way to have the "&" surrounded by no spaces at all.

EDIT: Further experimenting revealed a few more details -- on initial load of the plugin, it performs as expected (no extra spaces). But if you change any of a variety of parameters (font size, which fields should appear on the cover etc.) then the extra spaces suddenly appear.