I think there is a bubble but it depends mostly on location. At the moment here in Ontario Canada good collector pins are relatively scarce. If they do come up for sale they are usually gone in a few hours of posting.
But the prices here are really out of wack, An AFM in ok shape $6000, a TOM that needs every plastic replaced and a new DMD $3500. A beat up TZ $5000. AF in bad, bad shape $4000 You get the picture. It is not only the fact that collectors are holding onto their pins, but also the fact that the demand is way higher than the supply.
I am in no way a person who wants to inflate the price of pins but... I bought a Pinbot for $700 the same day the ad was posted, fixed a few diodes and misc stuff. shopped it added LED's and sold it for $1600 a year later, the same day I posted it, and that was to another collector. Just because they don't come up for sale,(at least not in that condition) and if they do they are beat to all hell and really only good for parts,unless you have a new Playfield but still $1000+.
The problem is Ebay price listings, and shops even if you tell a seller that it is not realistic, they still stand by that price. So really it is the actual shops driving up the prices of pins not the collectors, but if we sell for the actual realistic prices they end up being sold down the line for more later, either by a retailer who bought it after it broke on someone who couldn't fix it. Or someone who looks at the availability and waits for one of us suckers who just has to have it to come along.
You can find EM's for $200-600 all day long in good shape, but if a decent system 11 or DMD machine comes up prepare to pay a pretty penny. Any system 11 game $1000-$2000+ and when I give the low end thats for a machine that needs alot, ALOT of work.
Recently a non working pin 2000 SWE1 (not mine) with a bad playfield sold for $2500. WTF? I posted mine on a collectors site locally for $2800 or trade. Last run machine w/ plaque, New monitor, new playfield, mint cabinet, Full Led kit, etc, etc, and I have collectors offering me $1500-$1800. Again WTF? Just to see it up for sale a week later for $3000+. If I actually posted it for sale on craigs list or Kijiji it would more than likely sell, but I was hoping for a decent trade offer from another hobbiest.
Its frustrating, but true. So yes, the 30 somethings have a bit of disposible income now(I'm one of them) and guess what, because of this, the price will always go up especially in areas where the demand is so high, 4 million people in a 100 mile area around here means no reasonable prices. Or collectable pins left. But also they guys buying up loads of machines and waiting on them is driving up the prices too. Just like the last few NIB williams pins that have come out lately.
If it sold for that NIB, than my mint one must be worth this much.
But guys here have started going to the U.S. buying pins and flipping them at double what they paid with no other work other than border costs to the pins. Working or not.
Sad but true. Just my two cents on the subject.