If a residence has just been brought up to code
 

how long, typically, does it take for a HO to request an upgrade?
What are the usual reasons for this?

Thanks in advance.

If it has been brought up to code why would you need an upgrade?
I would guess it only gets upgraded (or even brought up to current code) next time some work needs to be done and only the stuff being worked on would be upgraded.

That's my question, and it's "need" or "want".
I could imagine adding a workshop or a much larger kitchen could be reasons.

Grab your wallet, do you "want" it full, or do you "need" it full?

"Want" is something you get over.

"Need" requires a little more effort.

Popping breakers once/month is probably on the want/need line.

However, I did lengthen the cord on the iron so it reaches an outlet on a different breaker. Same with our winter-use 1500 W room heater.

"Popping breakers once"

Which was not posed in your post.

Internet dentistry is getting the whole story, preferably before a response is requested.

My broader question is how should people decide to get an electrical upgrade or keep on making do.

The making do decision depends on how long they are willing to put up with problems or risk or inconvenience.

NEC's answer is, I guess, upgrade on each Code Cycle.

A service upgrade will not prevent breakers tripping. That is a products of the branch circuit.
It is a common misconception to think this.

Unless it is the very unlikely case that main breaker is the one tripping.

Which depends on the demand factor calc. being off.