The biggest benefits of the new generation, Quarq Elsa & Riken is:
1) improvement (reduction) in Zero Offset drift.
2) reduced sensitivity to chainrings (doesn't need recalibration when changing rings, and more chainring types are supported).
3) improved water resistance (but remains to be seen).
These known issues have been discussed for years at the Google Wattage forum.
However, for the sometimes very good prices the old stock is being sold at, "zeroing" the meter more frequently during the ride may be a good tradeoff!
Nashbar's price is now back up to $1400 + sales tax if you live in a state where there are Performance Bike retail stores ... 9-10% in Calif !
Nashbar's price would have to get down to $1000 range, to tempt me ...