That makes a lot more sense to me now!
Thanks to all who have offered advice here! A bit like railway modelling: it's nice to buy stuff and use it, but in more cases it's far more fun to muck about and modify stuff! I think it's the coming into simming from modelling (

) that makes me want to reskin, change sounds, modify routes, build routes rather than just download DLC and shout 'Isn't DTG fantastic - look at that awesome 7F they're still offering'. I look at stuff like the JT Bulleid, and want to enhance it. In that case I will buy the SSS pack, but I do get enjoyment out of learning how to modify and change stuff.
Therefore, I appreciate all the advice, help and assistance that people on this forum have offered.
All the best,
sem34090