I liked this idea originally, but the more I've thought about it, and the more *actual* migrations I've reviewed, the more convinced I've become that the problem isn't the voting - it's the posts themselves. 

If you have a question asked and answered on one site, then shoved into another (where, as you note, the culture may be rather different) the voting is really the *least* of your problems. Rather,

> A mediocre answer can get a lot of upvotes just because no one on the source site knows better. An easy-looking system installation question on Stack Overflow is sometimes a near-NaRQ on a more appropriate site like SU/SF/U&L, and yet it arrives with plenty of upvotes.

The answers are the problem. More specifically, an answer that's had time to collect a lot of up-votes, accolades, bounties, perhaps even an accept checkmark is a problem when it's seen as sub-par on the destination site. 

Like it or not, there's no way to implement a time-machine for migration that'll turn back the clock to when the question was originally posted. Resetting votes is - at best - a band-aid solution.

Therefore, I think the better option is to simply disable migration for older questions entirely. See: http://meta.stackexchange.com/questions/151890/disable-migration-for-questions-older-than-60-days