Are the gains of sublassing DBI over wrapping it worth the effort given my simple needs?

I doubt it. DBI's internal structure makes sub-classing quite challenging. I would sub-class DBI only when every other reasonable option is ruled out.

What do you want to override aside from connect()? If that's it then I'd suggest you not bother with AUTOLOAD, just return the DBI object itself! This has worked well on several large projects, see Krang's Krang::DB class for an example.

-sam