It depends, from a 'buying and selling GW' angle (something i do a lot of) it seems that recent plastics dont appreciate very well at all. People want new editions so sell those as soon as you can.
If you've got 80s metals they are worth loads at the moment,
90s metals (and some plastics) are appreciting in value fast, i'd personally hold onto them a little bit longer
90 or 2000s specialist games stuff you can pretty much make a mint on.
And Darius im with you on the masses of moulded symbols. it not only made stuff load smore time consiuming to paint but i hated the way its forces your hand in design. I much prefer lots of open surfaces i can paint my own images/crests/logos on.