Hi,
I just use my 420c when needed and don't ever think about the 'collector value' of it. It was my dad's, and I grew up with it around, and, well, it's still around.
Last weekend, I managed to get my JD 4500 4WD tractor/loader stuck in the mud at the edge of the pond (front wheels caked with mud and the rears just spun on the grass, so everything just spun and we went nowhere fast). I managed to lever it out using the loader hydraulics, but I had already got off the machine and headed in the direction of the barn (and the 420) before it occured to me that I could use the loader and save the trip.
You see, once you have a crawler, you tend to always think of jobs in terms of if it can be used or not! In my mind's eye, I could more readily see chaining the stuck tractor drawbar to the crawler dawbar and just yanking it out of the mud than I could prying it out using the loader.
One word of warning, though: Once you get a crawler, you start thinking about additional ones as well! :p
I'm looking for a JD450 with 6-way blade on the front and a scarifier/ripper on the back. That way I can have a big dozer and a small one and apply the correct size machine to the job! :p
Later!
Stan