Although I firmly believe Tolkien's work eternal and in the line of other great works through the ages, I'm also fairy sure the same cannot be said about the merchandise. Most things are selling for less than they've been bought for.
This is bases on my own experiences, and might not apply to everything:
(keep in mind I'm switching a lot between currencies here, mostly euro's and pounds, since I either spotted or bought things in that currency. And I don't have a currency convertor inside my head
)Even a bigger name as Weta is not immune to it. I got my Galadriel Statue without any visible flaws (there's a tiny chips of paint of on the part of her hand that goes beneath the gown) for 50 only euros. No one wanted to offer a higher price on her. (You can find her for 3 times that price on ebay, but keep in mind these are all BIN listings that have been listed for a long time.)
Arwen, though in worse condition, did only cost me 40 euros.
Getting back to the warhammer part, I see something similar. Everything that has come out with the BGiME is often common and does not have much value. With a bit of luck and keeping an eye out on these, you should be able to get the whole set for 50 euro's or less, for there are quite a few people who've long given up it and are happy to get a few bucks for it. If things from this have already been painted, it's often poorly done and you better give it away for free...
You don't see an expert paint job on these often.
Metal figueres seem to be the ones who keep their best value, followed by plastic, but the plastic figueres will not go for amazing prices as well, just decent ones and often not near GWs current price range.
Finecast new for new popular items seems to be doing quite decent. Otherwise it's not that great.
To give an example of finecast vs. metal: with a bit of luck and keeping an eye on things, you should be able to get an Elven Stormcaller for about or less what would the the price for one with GW, who GW only sells them in a set of 4 Galadhrim for £24
I've seen the metal version going anywhere for between £20-40.
The difference between this seems to be less with the really well painted models. Once the final result is alright, it seems to matter less wether it's metal or resin?
Having just stripped some metal figueres for the second time, I can understand people preferring metal quite well now.
And more on paint job, a badly painted common metal figure will rarely sell as well. Also, lot's sell at a cheaper price than the individual figures. Badly painted lots or lots with badly painted figueres sell even cheaper.
(which is great fun if part of that lot is a complete (old, so metal) White Council set, or has some 18 Haldir's Elves in it)
Of the the figueres I bought, Gildor Inglorion and the Galadhrim captain that has not been brought out in finecast are the only ones that did cost me quite a bit and I've seen Gildor alone going for prices between 40-50 euro's.
Others came either from GW itself, or for similar to GW prices (or slightly lower).
For many of the new Hobbit releases, I don't think many will hold their value. Now already, I bought the Palace guards, both Thranduils and Legolas and Tauriel from last years wave for their original prices, very well painted.
Now with more and more release being finecast, I don't expect them to hold their value as well.
It's hard tp predict how things will be in let;s say 50 year, but it could be rather that pile of coal than the pile of gold.