I did not read the whole thread, but having a similar problem, I did the following since an anonymous user was not asociated to the the default shopper group:
Have a look where virtuemart_user_id 0 is in #__virtuemart_vmuser_shoppergroups.
If so, set the virtuemart_shopper_group_id to your standard shopper_group_id.
If not, insert a pair (0,your standard shopper_group_id).
Perhaps this is missing when choosing a new standatd shopper group. I did not further analyze...