Because there will be plenty of tool authors there!
Yes, I think we should do both. Wikimania attracts a more diverse set of users (a lot more 'end users!') and I think a workshop here would be of a different kind than the one at Wikimedia hackathon, focused more on working closer with some end user who needs tools and building / fixing others to it.
I would also probably like to use this time to identify almost abandoned tools and recruite new maintainers.