Well, consider this. Pumpkins were spawning by the truck-load, everywhere.
For them to really be worth anything, you'd have to wait like 3 years or so and hope that none of the following Halloweens that no pumpkins spawn.
But even then, it still wouldn't be worth that much unless a majority of players toss out their pumpkins.
In a nut-shell. Sooooo many pumpkins spawned that it just really isn't that rare.
Now the dark colored pumpkins may be another story...
Oh brother. Let me tell you all the story of Caspian's biggest bust in UO.
No, I'm not saying that Power Girl was incorporated into the game at one point. I'm talking about one of the most foolish hoarding enterprises to ever be seen in Britannia.
It was around 2003, and the Holiday Gift were the Holiday Statues. There were such a wide variety, in so many different colors. Wow, sez I, this is gonna be for me. I'll just sit on them for a few years and I'll be swimming in the dough.
As of now (2009), they are STILL worthless. I regularly see Holiday Busts on sale for under 1k. Certainly, there were the very rare ones (gargolye statues, etc) that DO command the big bucks, but apparently, every Tom **** and Raistlin has their tower bursting with these things.
I ended up throwing out over 100 of these things. They are incredibly unlikely to increase from their current economic value of "bupkiss" in the NEXT six years.
Halloween pumpkins are the same thing. Everyone farmed the hell out of them over the past 3 years, and now they are worth next to nothing. Even the black pumpkins (the only one I bother to collect) aren't worth more than a handful of gold.