As has been said the memory itself isn't a huge factor, but when it's between a 6800 and a 6800GT, thats a difference in itself. The 6800GT has a more 'capable' architecture if you will not to even mention the extra pipelines of course.
The memory isn't so much a factor between those cards but simply the core that are used themself. The 6800GT could be 128mb and it'd still beat that 6800 because of it's architecture, extra pipelines, and GDDR3 memory which I believe the 6800 doesn't have.
So yes the $132 is very worth the price between those cards because it's not simply a matter of more memory