Jordan, I think you are comparing totally two different cars, ...and two different items regarding tools vs. spares. No one is saying they don't break down nor that you shouldn't carry tools but re-evaluate what is being said by others, then you.
First off, a Model-T is much more primitive in engineering and manufacturing than what an 'A' is. They are going to break with more frequency however there is probably as many if not more long distance touring done with the T's than A's.
Second, Ross is a very wise individual when it comes to things mechanical but based on the stories you tell, I refer you back to my first point. These deal with a much more primitive vehicle.
Now when I look over your list, I cannot help but question "why" on some things. I am relisting them taken from your text above:
a rubber mallet,
For doing what? Why not a regular hammer and be done?
starter,
Rebuild the one on the vehicle properly and then carry a crank!
alternator,
Again, a generator is easy to work on and reliable when properly rebuilt.
zenith carb (for others, i have a weber on my car)
Why? What breaks on a carburetor that cannot be repaired on the side of the road??
cotter pins,
OK but a length of safety wire serves multiple uses.
2 jugs of water,
Again, WHY?? Repair/restore the car properly and there is not a need to carry water.
a fan
REALLY? Why is a fan even needed?
tubes
A good spare tire can usually get you to the next town where there is a tire repair shop that can fix the flat tire.
distributors
I realize WHY is becoming a redundant word but why does someone need to carry multiple extra distributers? Restore the one in the vehicle and use it for 25,000 miles!!
fan belts
A fan belt should not have any tension. If the one on the vehicle is become aged, replace it and be done with it. No need to carry multiple belts either in my view!
hydraulic brake fluid
Surely you didn't just say that!! 
coils
I have never known a coil just to quit totally. They will generally work long enough to get you to town to find a replacement, -which when you replace it you will likely find that wasn't the culprit anyway.
other stuff i cant think of off the top of my head.
a full engine gasket set,
I have never known a copper head gasket that could not be re-used, and a small tube of silicone or Permatex can be used when the original gasket cannot be reused as-is.
torque wrench,
Hummmm....
Is this really necessary?
spare ignition parts,
I thought you already had several distributors??
trouble shooting manuals
?????
timing gear
I recommend if someone is planning on touring many miles, just use an aluminum and be done with it. For the price of the one on the engine and the spare one, it is cheaper to purchase the aluminum one.
timing gear wrench
See above, but in a pinch, a punch & hammer will suffice adequately.
a few other things.
wow.........
Jordan, I can honestly see how your brother would be frustrated wih you carry all those items. Like Tom mentioned above, what are you going to do if a radiator seam starts leaking? What would you do if the ammeter blows? What would you do if the gas tank starts leaking? Playing what-ifs and trying to prepare for each and every possibility is just a crutch in my opinion. Being able to make due with what you have at that time is what makes a great mechanic. IMO you have the ability to be a great mechanic, ....leave all that "excess baggage" at home and prove it to yourself.
BTW, I actually have toured quite a bit with Ross & Jennifer, Michael McDonald (and Rachel), the Cordes boyz, etal. Just was with them in Rutland Vermont a month or so ago.