We currently are receiving a very high volume of spam that does not receive any label in smartermail. My only alternative before going to postini is to increase one of these values from Zero which they are currently:
(since everything else is 10 and spam low is at 10)

SPF Pass 0
SPF Neutral 0
SPF Invalid Record 0

I am hesitant to up any of these since I have only seen one post on here where someone has increased any of these. Any recommendations on which one to try first? I'm assuming the last. Any insight is greatly appreciated. Thanks.

Leave all three at zero - none of them really imply spam. Here's a quick definition:

SPF Pass - SPF is correct, which means the sender is confirmed
SPF Neutral - SPF doesn't imply the sender, but nor does it fail
SPF Invalid Record - SPF record isn't configured correctly (most likely a mistake on their part)

If anything you'd want to raise that last value as you mentioned, however I would only do so on a VERY low basis to see what kinds of email get tagged by this rule.