Swap Wheels v Swap Tires
 

I have good knobbies that I hate to run smooth on concrete, and I have good slicks for street riding.
In y'all's opinions, should I spend several minutes swapping the tires? Or the several (guessing; it might be an instant Swap-out&Go) minutes adjusting the rd and brakes + wiping chain lube off my hands.
I don't have an extra wheelset yet. Matching wheelsets are not going to happen as far as exact same rims/hubs/etc, but similar cassette is no prob.

Swapping wheelsets takes seconds. Most of the time there will be no other adjustments needed with the der and brake.

Spare wheelset FTW. Swapping tires back and forth gets old fast unless you want the practice.

Get an extra wheelset. Keep it with slicks for city riding. You don't need to get anything really top notch, since the worst it will cross will be the odd curb. As mentioned already, it will take 2 minutes to switch over.

IMHO the spare wheelset wins, but if you have rim brakes I'd be careful to get a wheelset with similar width rims to your current set.

A spare bike is better still... IME a good MTB makes a lousy road bike, and vice versa.

I swap tires in about 25 minutes but wheels in just a couple. There's swapping tubes to think about too. Sucks having a 2.1 knobby tire on the bike and a 1.25 road tube in the tool bag.

It's worth having the second wheelset for bikes that will see some sort of dual duty. I travel with a hardtail, road wheelset, and mountain wheelset. I can ride just about any trail short of downhill or freeride. I can finish just about any road ride short of a century. It's the only way to go.

Make sure the cassettes and hubs are closely matched so there are no RD adjustments. Going from similar years of Shimano LX to XT, Mavic Cosmos to Ksyriums, etc. has never presented a problem for me.

If you have rim brakes, make sure the outside width of the rims match to less than a millimeter so there are minimal, if any, brake adjustments.

If you have disc brakes, make sure the hubs and rotors are closely matched so there are no brake adjustments there either. (I've yet to try wheel swaps with disc brakes though.)

I think I'll go for a second wheelset. Thanks for the reminder, I forgot about the rim brakes. I do have a road bike, but my MTB (Haro v2) I like to use on DORBA trails and goofing around in town. The roadie (Univega Gran Turismo!) gets MUP and road ride duty, unless my wife is coming along and then I ride the Haro.