What suffers the wear and tear are the vehicles themselves. The track if designed correctly should experience minimal if any wear. The vehicles at both locations have been replaced multiple times.
Just a small comment.
The WDW Monorails have only been replaced once in the history of the parks (40yrs). The Parks opened with the MKIV's and in the Late 80's/Early 90's were completely replaced with the MKVI's. The only trainset changes beyond this one mass-replacement were the addition of a passenger car to the first MKIV's (from a 4 car length to a 5 car length trainset), The addition of a couple new trainsets when the EPCOT Center loop was added (I want to say 2 new trainsets increasing the fleet from 10 Monorails to 12), And then the 2 new cabs recently to replace the ones damaged in the accident a couple years ago.
The DL trains have been replaced (I want to say) 4 times.... From the MkI to MkII, and again to the MkIII and then MKV to the current MKVIIs. While a couple of these replacements recycled existing mechanical components, They were still basically rebuilt from the frame up.
The Rails themselves at WDW were also (If I remember correctly) modified slightly when the MKVI's were brought online as there was a slight difference in the rail ride heights. (Though to be honest, I may be mistakenly thinking the rails were modified at the same time as the station platform height and Contemporary entrances for the larger trains).
That being said, The DL rails have had a major advantage vs the WDW rails. DL Trains don't run at nearly the same speed as the WDW trains. I think I remember reading that the max speed the DL trains hit is about 35/40mph during a short stretch between the park at DTD/
Disneyland Hotel station. The WDW trains routinely hit 45mph on the EPCOT loop.
The DL rails have also had some extended downtime to allow some basic maintenance on the rail and systems during refurbs in it's history...whether it be the extending the track from it's original in-park layout to allow the run to the Disneyland Hotel station..... Or when the trains have been shut down for trainset replacements or Sub Lagoon work.
The WDW rails in comparison have (especially over the past 10yrs) been running many more hours of the day year-round without any major downtime to allow for even basic preventative maintenances to occur. A couple hours overnight just doesn't cut it for how much those rails are traveled daily, which is one reason (besides the needed train work) we have seen so many changes in operational hours over the past year (No rails during EMH/ Midday stoppage in service/ etc).
There are also much different enviromental and track construction concerns between the two parks which make it hard to directly compare the 2 systems. It's easy to say "Attraction vs. Transportation" as the difference between them, but there is so much more to it than that.
