I think you show that you dont have to decide on one area and stick rigidly to it if you dont want to. At the end of the day it's a hobby and the important factor is enjoyment. It's about what aspect of this very broad hobby you enjoy the most. If that's collecting, train set operating or railway modelling (which has so many strands within itself to be honest, from nice scenery to watch trains go through to full operating procedure via parameters like operating accurate timetables) it's up to you and lines can be blurred between all three. I know for me it's a mixture of all elements.
Some people can be disciplined and limit themselves to one area, in one time frame, and only use stock from that period. I personally wish I was like that as I'd save a lot of money, but alas am not. I also see that the vast majority of people in the Irish scene dont tend to be like that too. It's an interesting comparison to the UK and US scenes in that sense as focus seems to be practiced by larger numbers there. I have lots of diverse interests but sure it's all part of the craic of it.