N=D-1 problem

This is why you always need a sacrificial bike in the fleet, when the wife gets fed up with 5 bikes clogging up the place you just sell the Argos Special because "you never get round to riding it anyway" and everyone's a winner.

Is it really the space or the fact that you have 2 (or more) bikes?

By selling one you aren't going to get much money and all you've saved is a bit of storage space.

Could you take the wheels off the Felt so it can be stored flat or take up less space? Or use some skyhooks or similar to get it out of the way?

If you really do have to sell one then keep the bike you prefer to ride (not necessarily the more expensive one). Also, if you ride through the winter make sure you keep on top of cleaning and regular maintenance, as the mud and especially road salt do horrible things to bike parts. Sometimes, having washed my bike and dried it off, I leave it on newspaper in the kitchen overnight to dry out completely.

I've got an old second hand carbon trek as a winter bike. THe biggest problem with it is that it can't run 25s. And if I attempt to put a raceblade long on the front wheel, gunk gets stuck under it. So I wear waterproof shoes instead.

As for components - you can replace dura ace with 105, so go for it, I say.

Buy a shed?

You need to slyly increase N by collecting more crappy bikes. Then when given the ultimatum comes to make N become N-1, N-2 etc... no heartache!

[[[[ If "The number of bikes....is causing friction", why not just change that number? Add another one.
P.R.

Cant you get rid of the person giving you 'friction'?

Whichever one you'd look forward to riding more in the winter is the one to keep - it's hard enough to get out when the weather is grotty - ride the one that will put a smile on your face. My riding buddy runs a nearly £3k carbon aero bike as his winter frame and puts his Colnagos away for the winter - it'll be on it's 3rd winter this year and he still kicks my butt every time we ride together

My thoughts would run along the lines of:
Which one am I less worried about dropping?
Which has the cheaper components to replace when the salt and muck wears them out?
Which one is more "resaleable"?
Also, just think how nice it will be getting back on the posh summer bike if the winter bike is not the world's best riding experience...