The way I looked at it was, I knew that as soon as I got the tractor, I'd find more and more things that I needed to use it for (not that the list was short in the first place). If I'd chosen a tractor just for the jobs I knew I had before, it wouldn't be long before I was pushing the limits of the machine.
Buying a bit bigger & tougher gave me a year or two more headroom before I need to get a really bigger one!