I asked myself the same question and I decided its not worth it (For me that is, it might be for you
), not if you plan to go with the G10 anyway.
The Viera Cast could be really cool but I dont think I would use it very often anyway, and if it turns out to be great then I will just get a Panasonic Blu-ray player which is cheaper than the price difference between the G10 and G15 in my country.
Besides I dont want to wait 2 more months.
Unless there was some great improvements in PQ then I would probably consider it.
As well as going for the V10 if it would be produced in a 46" model, because 50" is just too big for my room.
Oh well, makes the choice alot easier
Edit, the 24p/96hz thing sounds good though, but isnt that the same thing the UK type G10s already can do?