If you are collecting to gather a 'nest egg' then IMO you are in this for completely the wrong reason. This is a hobby, it's meant to be fun to collect the things you love.
As long as you are happy with a purchase you are making at the moment, that is all that matters. Some pieces
may increase in value over time, some
may not, This is not the stock market so if you want a guaranteed return, I would suggest investing instead.
Enjoy what you buy, if something makes you happy today, that is the main thing. I don't think anyone can predict what the aftermarket value of any collectable will be in 10 years time. Even the big hitters from the days of SSW have prices that fluctuate, nothing is guaranteed and no-one can know what item (if anything) will be worth a lot in the future.
Buy what you like, and like what you buy - that's the most important things in this hobby, imo.
Just my thoughts anyways.
x