I think much depends on whether you believe the sailing season has ended, or whether the cooler temperatures and steady winds of spring and fall make for fine sailing. In my opinion, this September has been much nicer than June, July, and August. A nice day in February can be magical. In fact, I was sleeping on the boat during one of those blizzards, the heater running, enjoying the silence (sort of an accident really--I was returning from a business trip and the marina was on the way back). I sail all year and love it that way.
You say you will haul in the spring anyway. Can't say. I haul every 2 years, but I do it in the summer in a single week. The notion that many projects can be worked on over the winter is just plain false in many (not all) cases.
* You can't paint or epoxy when it is cold (below 50F at night can be a problem). You can do it faster in the summer.
* You can do most jobs at the slip just fine. Unless it is through hulls, the bottom, or painting the sides, you can do it afloat.
* Often little projects done during the summer are more pleasant than one big push in the spring. A little something to do, after work. A lot less climbing up and down a ladder, but perhaps a longer walk to the car. Personal taste.
Some say the boat ages less if hauled. Perhaps, but...
* I've had a stand go through my boat. A boat is better supported in the water, PARTICULARLY when there is heavy snow. However, you do need to be certain all deck drains are clear.
* Frequent use protects many items. If you sail all year, batteries stay up, lubricants circulate, and electronics get dried.
* A boat on the hard reaches 15 inside, at least a few nights. A boat in the water only rarely goes below freezing, and then only a bit. The water keeps it warm. Winterization on land is actually more difficult, IMHO.
I like to consider my cost per use. If I sail 3 times per month for 4 months, she costs perhaps $500/trip. If I sail 12 months and go on some cruises, that cost may be only $100. Or more simply, the off season trips are free.
A longer post is here. I've been in the water 25 years in a row, ever since the stand incident (the marina made it right, but I still lost sailing time). I've never lost more than 3 weeks to frozen water, but that varies with the marina (some get little tide and much fresh water).
http://sail-delmarva.blogspot.com/2009/12/winter-sailing.html