Damien,
Think about it as this relation Porsche 997 Turbo>Porsche 997 GT2. R8 V10 will use same side blades and marginally different side skirts then current R8, also both front and rear vent will use three big vents. So, changes will be(exterior) marginal(oh, I forget V10 signature on same place where V8 is on S5). Price wise R8 V10(yes, it is official name-you will see it pretty soon) will be around €25K more expensive in Germany then current R8.
BTW, Leadie was right(cheers man!)! Technical stuff on R8 V12 TDI is pretty amazing...