I agree that it's great that at least one has been preserved and by a great organization that's dedicated to preserving transit and trolley vehicles.
Growing up I had the opportunity to ride and see these cars, at least on the MBTA. The MBTA blue line also utilizes catenary for its outer-most service to Wonderland Park in Revere. They kept the ROW (The line is now standard gauge today) and catenary service of the former Narrow Gauge (BRB&L) line when they opened the service to Logan Airport in the early 1950s. It seems that the salt air is detrimental to the third-rail system so it's better to run with pantographs which come up just as they exit the tunnel at the airport station. These cars were replaced in the 1970s by some Hawker-Siddley cars, which are similar to the same on the orange line, but are really short and narrow compared to the older cars. These have been subsequently replaced, or being replaced by some Kawasaki cars.
I read about the CTA/CSL street cars being made into heavy-rail cars. You can see the similarities with the side windows to those of PCC trolleys.
John