I am a diamond select. Exclusive rates mean that you will be charged less than someone just coming in or making a reservation on the phone who is not at BW rewards member.. however, Priceline for example can offer cheaper rates than the hotel itself. So you might want to investigate them for the better rate.
Free upgrades are no longer a given and not even advertised on Best Western site as they used to be. That was one of the advantages I liked. Also, I stayed a lot on the road and would accumulate enough points to get free nights.
If you're looking for the best rate I would check out Priceline just to compare. Best Westerns are independently owned and I can assure you the quality varies from hotel to hotel.