This is what I did and everything updated just fine by following the guide in OP and his "updater-script".
From rooted wifi xoom, I backed up everything.
I returned wifi only xoom to full stock
Rooted wifi xoom using one click method
Followed the instructions in OP to update to 3.1.
Installed root explorer and gave R/W permissions to everything.
Installed Busy Box and gave SU permissions.
Installed Titanium Backup and batch installed all my apps and data.
Everything is working fine for me so far.
Thanks for the great guide & script stachre!!