Found a certified base 370z with upgraded heated and leather seats...should I?

[Cagan]

My fiance and I have been looking for quite a while to find a decent 370Z. We really wanted the Touring because of the sound system and the heated seats but we just can't find one with the right price. We found a really well priced base 2011 370Z with 12k miles. Its certified and the dealer upgraded the seats to leather and heated. What other things besides the sound system are involved with the Touring? I understand that the Touring has 8 speakers instead of 4. Would it be just as good to upgrade the 4 speakers aftermarket? Will 4 upgraded speakers (spending ~$500) be just as good as the 8 speakers that come with the Touring? Are there any other options that the Touring has that are really worth having? Any advice would be greatly appreciated. Thanks.

EDIT: Also, it doesn't come with nav. Would it be worth asking them to upgrade the nav or would it be better to get an after market one? Is there an aftermarket nav that's better than the OEM one, goes in that same spot and looks just as slick - or more so? Thanks.