I think you are greatly missing the point:
The user does not need LAST year's AGI, she needs THIS years AGI because Intuit, in all their infinite wisdom, does not allow you to leave your spouses AGI blank when MFS.
I'm no tax expert, but I am able to read the actual 1040 form and instructions, as well as supplementary info and all signs point to not having to enter your spouses AGI when MFS.
I didn't contact the VA Dept. of Taxation, however they do have a MFS option and it does not require you to enter your spouses AGI. I don't believe you are allowed to file single if you are Married and your state return has to match your federal filing status in VA.
Once again, I'm no tax expert, but my insight is provided by my reading of the instructions they provide for completing the tax forms.
Thanks for following up though, what filing status did you file your federal return? I'm curious because of my current situation.
I wish Intuit would provide an official answer to requiring the spouses AGI when MFS since the discussion forums here don't explicitly provide fruitful guidance.