We managed to see the disguised pre production cars running round the R&D centre when we were there. Basically the car is so heavily taped up that you cannot tell anything much other than the fact that the side air intakes are now much more rectangular and less organic and that the interior would look like the cayenne/997 type. Not sure about engine sizes but I would imagine that the finished product will be like the 997 vs the 996. Majority of the components have been improved so that they can say that the car is >70% new but the looks will be an evolutionary change. The company is extremely conservative and you can be sure that the new product will be quicker but safer etc.
Don't think you will ever have a 'bangle' type of revolution in the way they do things cos they are just too conservative. IMO, that is a good thing..
In terms of how much, I would imagine a small increase in price vs the current car. Like 997 is asking $480k and $510k (997 and 997 S) vs around $460k for the outgoing 996 C2 coupe. So dont expect any change from $300k for the new Boxster.