Dont really think the hobby is dying. I suspect its more "changing of the guard", with people getting burned out, new people getting interested. Locally here, Ive met as many people starting into the hobby, as Ive met getting out of the hobby. Most of the folkes I know leaving the hobby are doing so because of life catastrophies or economic difficulties. Dont really think the prices are going down so much. You cant really base prices pitched here as market. There are those of us who like a restoration project for cheap so that may skew the prices a bit. I'll tell ya this, they aint makin any more of em. Nice restored games, will hold their value. Im almost 40 and Im finally financially and logistically able to have some games. Several of the new folks Ive met and helped are in their 20's, so thats encouraging.
Yeah, I'm 36. And I plan on fixing, restoring, collecting and PLAYING my games until I'm dead. So with any luck I'LL be in the hobby for another 50 years.
This hobby isn't going anywhere. Just because the money isn't flowing like water right now doesn't mean the well's drying up. Many guys like me will continue to spend disposable income on their games.
To answer your questions, I'll put my opinions in on your list, based on what I've seen lately:
1. Original working Pac-Man Upright
Depends on artwork. Minimum $400, probably more like $600.
2. Tempest Upright with dead monitor, plays blind
Non-working cabs are tough to price. Again, as stated above, artwork is important. If it's got an Amp monitor, then it's worth $400. With a Wells Gardner 6100, it's worth less.
3. Original Ms. Pac-Man with unknown condition
Unknown condition? Hard to say. With good artwork, it's worth $200-300 if it's complete, but not working. Missing any parts and the price declines.
4. Original working Popeye Upright
$300
5. Original working Assault Upright
$300
6. Original Asteroids cocktail
Cocktails are hard to sell, but to the right buyer, they're worth good money. $400.
7. Original Zero Hour cocktail
Working? $250
8. Original IPM Invader cocktail
Tough to price. But working, I'd say $500 to the right buyer, depending on condition.
9. Original Tekken Upright with unknown condition
Dedicated Tekken is worth $500 working, maybe $200 complete, non-working.
10. Donkey Kong project with all but PCB
$350 if the monitor looks good and the artwork is complete.
Total: $3900 best case. I'd say a good offer on the complete package would be $2500.