Yes, I do own three 2014-2015 xB's with the same engine, tires and transmissions. I record the vehicles data in spreadsheets including average temperature. Here's what I got from my transmission maintenance experiences.

1. 2014 105,000 miles Transmission Fluid and filter Replaced at 100,000. Vehicle had normal minimum maintenance by previous owners. After the transmission fluid and filter change there was little difference in the slightly slipping gear shifts. This one does deliveries.

2. 2015 105,000 miles Transmission Fluid and filter replaced at 90,000 miles. Vehicle was well cared for by previous mom with kids owner. After the transmission fluid and filter change there was a slight improvement in the gear shifts. No real slipping and smooth during acceleration. My wife stole this one from me so I had to get another one.

3. 2015 65,000 miles Transmission Fluid and filter Replaced at 63,000. Vehicle well maintained for first 45,000 miles,then 15,000 of sporadic records. Original TRD 19" wheels replaced with Toyota standard 16" Alloy due to an un-hip new owner. Although the trans had no real issues I felt it would be best to do it. After the transmission fluid and filter change there was a slight improvement in the gear shifting.
I was pleased to see first gear into second is quick and smooth and going into 3rd and 4th is so smooth that I need to watch the RPM's to see when it occurs. I am also getting over 5% better miles per gallon. That improvement may be due to the more solid shifting during the vehicles normal heavy stop and go traffic driving. I don't let my wife drive this one.

All the shops doing the work had reservations on this filter/fluid replacement and warned me each time that sometimes the metal in the fluid helps keep the trans from slipping. If that is true then maybe straining the old fluid and putting the magnetically separated shavings back in would be a fix for those worn transmissions. But I do not quite understand how adding wear agents to a fluid could improve function.

What I get from this experience is the sooner you replace transmission filter and fluid the better things go. So most likely changing a vehicles filter and fluid at 30,000 the first time might cut down the floating metal and accompanying wear. Unfortunately, finding a Scion xB with less than 30,000 miles to test this theory will be difficult.

 

I had a 2000 Honda v6 from new and I changed the AT fluid religiously, with Honda fluid, every 30K miles, along with a filter and cleaned out the pan. Gave it to my daughter around 90K and I kept up with all the maintenance still, yet the tranny failed at around 110K. I read that Honda found out thru customer focus groups that they didn't like the rough / abrupt gear changes, so they put in something to slow down the clutch engagements. This caused the clutches to slip too much during engagements and they slowly wore down over time. It was unfixable without a new tranny, so they ditched it for another car.
One of the many reasons I will never buy another Honda.

Debris in the fluid will not help anything in the transmission and can can block passages in the hydraulic computer that controls the transmission. Debris can also mess up bearings.
If the plates or bands wear down, it may have been designed that way, or a change put in that overruled the engineers (by salesmen).
Keeping the transmission clean is the only thing we can do as users to help the transmission last beyond the warrantee lifespan.

IMO for regular automatic transmissions, that means a pan drop, filter change, magnet & pan clean every 60K miles.
For a CVT's (except nissan) that means a pan drop, filter change, magnet & pan clean every 100K miles.
For some cars that do not have sump pans on the transmission, you are kind of stuck with what the salesmen have decided.