Great thread everyone, thanks for the contribution.

I have seen puncture protected inner tubes.... Really?

Yeah, ones called thornproof - they're really thick on the outside, so more difficult for nasty pointy bits to penetrate.

They seem like more of a weight penalty than Mr. Tuffy, so I'm not into them.

Then there are Slime tubes. Work OK on low pressure tires. They do require a bit of work to keep the slime out of your pump and from clogging up in the valve. I used to run those in the desert, good against goatheads.

1. The same for either. The wider tire has a little more grip, but it's not significant in normal riding - 1.5" is already very fat compared to a road bike tire.

2. The same.

3. Fatter is better. 1.5" is comfortable though, I wouldn't do 1.25" that's to skinny in my opinion.

3...b?. Skinnier is better. 1.5" -> 2.0" is probably going to increase tire weight and rolling resistance enough that you'll notice.

5. Same. Might vary depending on your particular bike.

A bigger tire size (700c, rather than the 26" you have now) will be faster, smoother, and grippier at the same size. So...yes, I think it's worth it.

You can buy a cyclocross or touring bike that's a road bike, but with enough clearance to take fatter tires, if that is a priority. I will say though that even just 25c's with good tires (Continental gp4000's) have been good enough for me.

Regarding your other question, yes, flat resistant tires are always worth it. I can see no reason outside of racing on a closed track to ever use a non-flat-resistant tire. You don't have to spend a ton of money - Panaracer TServ tires were $35/tire and worked very well for me.

Schwalbe Marathon Supreme and Kojak. Kojaks are lighter/cheaper,Supremes are grippier/more puncture protective.

I ordered a Cheng Shin C783 to try a street tire on the rear wheel of my MTB, with studs in front. I only had that tire on there for a couple weeks, before switching to 2 studded tires, but I was quite pleasantly surprised by the ride. FWIW it's 26 x 1.5, rated at 65 psi, has moderate tread, and is 13 bucks at Niagara. My riding is all paved streets or MUP, not super fast, pretty tame terrain.

You might be looking for something higher-end, but I think this C783 deserves to be mentioned for folks who are trying to put an old MTB into commuting service without breaking the bank. The Cheng Shin 27x1-1/4 road tires on my regular commuter have held up quite nicely and seem to ride just fine.