First things first. There's no such thing as a dumb question - only dumb answers.
but don't seem to have these dilemmas.
Of course you don't have these dilemmas - you're at home, or going home. One of the liberating things about a bike tour, especially a long one, is that we get to make a new home every day. The bike might be packed a little heavier on tour, the scenery might look different, the weather will hopefully be different, the language might be different, but the real, substantial difference is between our ears.
A strange sound coming from the drivetrain 5 miles from home isn't a huge cause for concern, that same sound in the Atacama desert might be!
how do you manage being on the road so much of the time?
To your main question.......
As with so many things ...... It depends.....
There are different kinds of touring.
There are tours in different places.
There are tours with a different focus - eg 400km in two days Vs 400km in 10.
There are different kinds of bikes & gear. Some are more tolerant of improvisation than others. (My bike will operate with a 7 or 8 speed cassette as an example).
There are different kinds of people. Some will become frustrated if they are not moving far or fast enough. Others haven't a clue about bike maintenance and will happily ride until their bike breaks.
For me, ironically, the bike is probably the least important thing on my mind most days. I do basic maintenance, mainly to do with keeping the chain clean and tyre pressures appropriate. Adjusting brakes or replacing blocks when necessary.
Bigger services occur when I have a chance or when the situation demands. Roccado is like an extension of me. I think I can generally feel when something isn't quite right.
My camping gear needs attention, as do my clothing, tech etc. And I need attention every now and then. It's not just the bike.
That's why I always encourage newbies to forget about getting a fancy bike until they're sure they know what kind of bike adventures they want to have and where and they start to see the big picture of how everything can link together.
I'm not sure where you are seeing the rapid wear of components but if it's online then you ned to remember that people have different levels of fussiness about these things, some like to be the "Internet Hardmen" who like to tell people why it's all gone wrong and why it'd never happen to them and places like this are for discussing. So things get discussed.
Remember, there are far more people out there riding bikes and having bike adventures than ever post online.
The big factors in what to cover are probably addressed by availability and comfort.
By availability I mean the availability of components where you plan to travel. Urgency may be a sub-factor here too. (I can buy pretty much anything on my phone but getting it to me might take a while). As perhaps is cost. Some countries can be ridiculously expensive for parts. If no components are available (or affordable) then you may need to bring some. Simples.
Then there's comfort. If not carrying three spare tubes will make you nervous and uncomfortable then there are two choices. Face down the source of the anxiety head on or pack the three damn tubes!
There's no point in being on tour and constantly anxious. At least in my world.
Weight is usually bandied about as the premier issue. As should be no surprise at this stage, I don't give a fig about weight. I want to know that I can deal with whatever I need to or choose to face. Being X km faster means little to me. Going X km further ditto. Being comfortable where I am and where I'm going is what is important - to me.
(I'm convinced that a big factor in weight being deemed so important is that it is measurable. And comparable. My rig is X kg (or God forbid, grams!!) lighter than yours is much easier to discuss than I enjoyed that place more than you. What is the unit of measurement of enjoyment anyways?
And a focus on destination. How long will it take, how hard will I have to work to get to X over how will I enjoy the journey? )
You may have noticed by now that I rarely use the word "Tour". I am bemused by the idea of a "Touring Bike". "Tour" means so much to so many people, yet has very different meanings to so many people that it's a bit of a useless word. In bike terms, a "Tour" may not too different to a series of your usual bike rides. Do to the bike what you usually do when you usually do it (but be aware that may be a little more difficult than at home).
Of far more importance to me than spare parts and toolkits are the tools to keep my head balanced and tuned up.
Sorry, that's all about as useful as the proverbial chocolate teapot and perhaps I've proved the "only dumb answers" thing
The most disastrous mechanical things to happen while adventuring on the bike away from home are:
A pringled front wheel and murdered dynohub in a drain (led to a life affirming encounter)
Losing three spokes in one day (that was a long walk!)
5 punctures in one very, very hot day. So hot the damn patches wouldn't hold. (Led to one of those moments that reminds me how lucky I am)
A cassette damaged by a stone - was able to limp on to the next town.
A broken saddle pin (lead to a wonderful Italian encounter)
A sheared off rear derailleur caused by my own dumbassness.
A broken rear rack dropout, welded by the local welder
But to put things in perspective, I set off on my first, solo, unsupported tour without a puncture repair kit - but two panniers half full of books!
There was no point in bringing such a kit because I didn't know how to use it! I can read, though
Of course, Murphy's Law kicked in but so did my luck. A very pleasant German not only fixed my puncture, he patiently showed me how to do it (without once being unkind) and sold me a puncture repair kit.
If I had waited to go until I could fix a puncture, well, I might still be sitting in NL.
