It may be in their fine print that they only give you current market value, but in my experience they have always replaced like for like, or like for similar specs (and macbook pro for macbook pro, macbook for macbook, etc.) If that doesn't work, they have also just given me a "credit" for the original purchase price of the unit, which I could then use towards the purchase of any other system at Best Buy. I think the accidental protection policy may be worth it from them, but based on reports on this forum and throughout the web, BB warranty is so dependent on the BB you take it to, the geek squad person you speak with, etc. So YMMV.
My advice would be to get the BB warranty. Remember that you can cancel it at any time, and you will be able to receive a prorated refund. You also have the ability to purchase Apple Care within the 1st year. So try out the BB warranty during the first year (if something breaks, etc. take in to BB and see how you like their service); if its not satisfactory, you can still cancel it and buy the Apple Care. Your net loss may be around 60-70 bucks depending on how long it takes for you to need to take your system to Best Buy.