Colin,
With a few grand into an E55 you can get those bad boys to over 500whp...That's no slouch at all. EC just did 180.5mph in a 55k car at the Texas Mile. Can't complain about that.
As for talking your wife out of new car fever into favor for a 2006 E55....just offer to give her a shopping spree to accompany the car. I mean you would be saving $30k, so giving her a few grand for whatever she wants will ease her pain.
p.s. I also vote E55 > CTS-V.
Hell right now you can do E55 + SRT6 for the price of a new CTS-V.
There are plenty of E55s out there right now with under 30k miles for right around $30k.