I agree that a lot of those threads could get very very long due to the size of collections...and unfortunately they may not get too much attention.
A personal list on something like Klect or an online spreadsheet is no doubt the best option for you to keep track. But if you did wish to post a list of the ponies you have, its perhaps more fitting to the Brag Arena - which is where people should show and tell rather than the Corral that is intended more for pony discussion.
There is also a long "show me your collections" there floating around the first few pages of the Corral - that is a collective show thread - perhaps looking for that will work for what you wish