I think it goes on a company-by-company basis, personally. Or even by specific license. I remember when ThreeA first started and were producing relatively tiny production runs their stuff went for crazy prices on the aftermarket, unless you were lucky enough to be a member of a community like KidRobot who'd sell to other collectors for more sane amounts. Now there's very few items they release that don't either hang around on the aftermarket for retail or less, or in the case of items sold through retailers, end up on clearance at some point.
Look at Hot Toys circa 2011. A lot of the stuff they released around that time soared in price on the aftermarket, and has still largely held its value. If you want some of the early marks of Iron Man suits, Avengers Loki, Batsuit Begins, Tech Noir Terminator, DX13, etc you're looking at significantly inflated prices even now. There was a palpable sense of excitement in the community around those releases, people went all-out to complete the Iron Man Mk I-VII lineup, get halls of armour for them, get all the Avengers figures, and so on. Then Hot Toys started cranking out Iron Man suits that had anywhere from two minutes to less than a second of screentime, constant reiterations of Captain America, Black Widow, Hawkeye, Thor, and other characters besides. Less emphasis on 'cult classics' in favour of the flavour of the month. Couple that with larger production runs, better distribution and latecomers jumping into the game thanks to sites like Kotaku raising awareness of Hot Toys' existence among people who weren't traditionally collectors and you have a saturated marketplace. I picked up the Iron Man Mk 33 Silver Centurion for less than £100 brand new last year, which is just insane.
The only figures that seem to have escalated in value recently from Hot Toys have been their OT Star Wars releases - so naturally, they're doing an unprecedented second production run. I'm not complaining, you'd be a fool to collect toys as an investment opportunity (put the money into stocks and commodities instead if all you care about is a return five years down the line). I imagine Hot Toys don't care about the aftermarket flatlining (in fact I can see Howard grinning ear-to-ear that nobody can make more money than him off the company's products) as long as their stock sells out to their international distributors and the local Hong Kong population keep buying.
I'd say the collector's bubble has largely burst outside of a few figures each year that, for whatever reason, go up in value. 1/6 in and of itself will be fine for the time being, though - although I don't feel the same excitement for new Hot Toys releases that I did back in the golden old days, that's for sure. Since releases like the Iron Man 2 figures, Batsuit Begins, various DX releases, etc it's very much felt like evolution, not revolution. Nothing has improved as significantly as the leap from what came before to those figures since, the innovation curve seems to have levelled out.
I predict hardened collectors looking for something interesting and representing good value for money are going to start getting into quirky original lines like Gangster's Kingdom from DAM more as the larger companies like Hot Toys and Sideshow edge ever closer to the $300+ mark for a barebones licensed 1/6 release.