Chatgpt agrees. Electrical load has a negligible effect on the wear of brushes or any other components of an alternator, so long as temperature is within spec.
You bring up brushes, which is a good example. They are wearing out faster running over the rings than any electrical process could. Technically speaking all electronics can wear (so to speak) eventually at an atomic level but what is much, much more common is environmental damage (either directly or creating a cascading electrical failure) from heat, moisture, vibration, impacts, etc.
The roundness tolerance on the ring manufacturing, which fatigues the springs and causes non-uniform brush wear is worse than asking them to carry high current. So, yup, alternators are killed by heat, fine dust, water submersion.
Now that said, electrically there are limits to the size of the brushes, slip rings, winding wire and diodes. So I am making an important presumption that at rated current the designers anticipated how to get the heat out. But as long as you keep temp/current/voltage at or under 100% of the rating electronics aren't wearing significantly faster than they might at 10% or 50%.
Plus you have to obey physics. So adding a computer fan isn't going to get you tens of amps necessarily. Consider how much air is moved traveling down a highway and mimicking this could require a fan that consumes a non-trivial amount of the extra power you generate.
Let's say you find your 170A alternator is getting pretty toasty at 60A idling. Remembering, too, that regardless of heat an alternator output is dependent on RPM, so even ideally cooled it won't necessarily achieve full output until you get it turning a higher RPM anyway.
Just for the sake of discussion you find asking it to give you 60A is where the case (or if you can find the actual winding or rectifier or regulator temps) hits the specification limit. You find that moving the equivalent of 25 MPH air over it allows 80A safely but to do that electrically takes a fan that consumes 10A/120W. You're only getting a net of 10 amps more, the loop has to close electrically and thermodynamically. In the case of modern cars the radiator fan motor turning on could consume a lot of your alternator's power at idle, for example.
BTW, that brings up another thought. Often the OEM under drives alternators. Alternators like to turn around 2000 RPM and faster and so to get this they will use a ratio to the crank, say that's 3:1. At 700 RPM idle the alternator is turning 2100 RPM. But the problem is the upper limit. At redline of 6000 RPM you're now asking the alternator to turn 18,000 RPM. This might limit the bearings and generally is tough mechanically. But if you can cap your redline you can sometimes justify a slight ratio change, 3.5:1 or even 4:1, to spin the alternator faster. This helps not only bring up the current at the low end but since most alternators have a built-in fan it helps with cooling, too. But you really have to watch redline, you definitely do not want bearings seizing when you try to merge in traffic trying to not get flattened by a cement truck.
