I have to say that Mike has hit the nail on the head with his comments about the desirability and value of team index bats, and bats that don't match factory records.
As a long time collector, I have purchased quite a few bats that don't match factory records or known characteristics (way back before we had all the records we have now). But in each and every case, they would cost considerably less than a model that was deemed to have actually been used by the player.

With many new collectors coming into the hobby in recent years, I find that for the most part the above still holds true, and then some. The impression I get is that most of the newer collectors are much more adamant about getting bats that match factory records -- they don't want non-matching bats at any cost. I think it's in part because they realize they still have a lot to learn about bat nuances, and they're also thinking about resale if their collecting interests change down the road. Mike mentioned that some of the high prices for team index bats may be coming from uninformed collectors, I would submit that they also may be collectors with vast financial resources who just don't care much about price (it only takes two in an auction).

A good way to check all this will be to follow the course of about a dozen bats put up for auction by one seller on ebay this weekend. All have buy it now prices of four figures, yet almost all are model numbers not used by the players.
When it comes to off brand bats, I think collectors of all types will only pay a premium for them if the leading authenticators give them their seal of approval.

As for Rod's post about the Reggie Jackson bat, while it is very well thought out, I would respectfully take issue with two things. Collectors are much more likely to take a chance and pay more for an undocumented or team index bat of a player whose bats are much more hard to find and much more expensive, and are from a much earlier time period where the records are more sketchy. There's no need to pay a high price for a team index bat of a 70s player whose bats are plentiful.
As for the idea that you can't prove a player did not use a bat -- it's important to realize you can't prove a negative. I could take a Joe Pepitone bat and never be able to prove that Mickey Mantle didn't use it. You could spend a lifetime looking at thousands of photos of Mantle, and even though he was never holding a Pepitone bat, that still wouldn't be proof that he never used one.
The bottom line is that collectors should always try to make informed decisions, and buy things that make them happy and fit their budget.

Greg