I'm going to be a wet blanket w/ my answer. If you can rebuild the machines, I think that would provide you the most stable "known quantity" environment. Unless the applications are such a huge time sink as to cause a "migration" to be a net win, I'd think that the time spent making the migration solution work well could eclipse the time just to rebuild by hand (and, besides, it's probably not a bad idea to use this as an opportunity to create or refresh the documentation of the configuration of these server computers).
To my mind, migrating a 3 y/o Windows installation means migrating a lot of old hotfix uninstall files, potentially garbage files and registry information, and a general "cruftiness". Unless you've done a really good job keeping these machines clean, there's probably some of that cruft that will migrate over.
OTOH, if you've got a particularly touchy application and this is a "known working" environment that's been highly tweaked you might see a net win in migration. I'd play devil's advocate and say that all that tweaking should be documented and reproducible. >smile<
I guess it comes down to how painful it is to rebuild the applications and transfer the data. The OS and drivers should be easy and a non-issue.