I'd say stick with the Seven. In 10 years it will be worth a lot more than any carbon bike you buy now. Replace every wear item in the drivetrain. Cogs, rings and chain. Look at your derailleur pulleys. Have a wheelbuilder make you a set of really nice wheels for special days and ride the Ksyrium as everyday wheels. New bartape, cables and housings. Brake pads. New tires. Bike will feel like a brand new bike. You will be in love again, will not have broken the bank and your bike will truly shine, both in looks and on the road.

A guess on the cost: Wheels - say $1000, drivetrain - $220, bartape, cables and housings - $40, brake pads - $12, tires - $150, misc - $75. Total - $1500.

You could upgrade to n+1 cogs but for two sets of wheels, this may not be feasible or cheap. I'm guessing you have 9-speed. 9-speed works very well and gives you a great range of choices. As long as your rear derailleur is doing its job, I'd stay there. (And if I saw another rear derailleur in my travels, I'd grab it.)

Ben