Winter tyres or winter wheels? I've just picked up some lightly studded tyres - winters aren't too bad here but ice can be a problem.  The bike is a hybrid mainly used for commuting, with some early starts.  Most of my route is theoretically salted, but not all and not always.  I'm planning to mount them this weekend on the rims I've got, so this question is thinking ahead to when I put my normal tyres back on the bike. The bike in question is a hybrid set up with a not-easily-removable child seat, so must do duty all year round.

Does it make more sense to swap the tyres or the whole wheels?

I've thought of several reasons both ways.  In favour of swapping wheels:


Rims, cassettes etc. wear out anyway, so I'll have to replace them at some point (the rims have >5000 km on them).
I can put the summer wheels back on if I'm going for a long ride on a warm day. (I now have other bikes for this so it's not an advantage any more).
Over the course of a year it's less work to leave the tyres on the rims (3 season tyres are marathon plus so not the easiest to mount, but not the hardest either).


In favour of swapping the tyres on the rims:


Save a little storage space.
Defer some costs.


and the two big ones:


Will I have to align the derailleur and/or brakes when I switch wheels?
What effect will running a new cassette on a worn chain have? Alternatively: when do I need to swap the chain if I'm running 2 cassettes of different ages.


What experience do people have of the last 2 points in particular?  Is there anything I've missed?
I'm assuming you have rim brakes, since you are asking about wear and aligning brakes.


Winter riding will wear out everything faster. The rims are going to be wet and dirty for most of the time, and the same goes for transmission. It might be a good idea to use any old equipment you don't care about as winter parts. The exception is that better hubs have better sealing. 5000 km isn't that much for rims, by the way.
Unless the rims are exact same width (or the rotor is aligned exactly the same) you'll have to adjust brakes every time you switch wheels. Possibly the derailleur too.
New cassette on worn chain will be noisy, wear out the cassette fast and skip if the chain is worn badly enough.