I think with a lot of trades it is more about the personal value you place on the item. If you don't care that much for the snowman and really really want the river chair then do the trade and enjoy your new chair (actually chairs I guess).
For me personally, the snowman was a very limited quest item and we just don't know how soon the thrill seekers quest is going away. The river chairs are hot now because they are new but they could become a more common quest item the longer they hang around (something like an Ace of Spades carpet). I would hold onto the snowman and see if I can get a better deal on the river chairs in a few weeks. I would speculate that you will always be able to trade your snowman for the river chairs so there is no downside to waiting it out a bit.
Remember when the first Narnia telelporters showed up people were talking inferno trades for them. Their stock seems to have gone down quite a bit in just a week or two.