Originally Posted by Psychic Pimp
There is nothing horrible about the Sora crankset, I would wait until something wears out myself. You will probably see a bigger performance difference over time upgrading from a Sora to 105 derailleur.
If you are thinking of switching because of the chanring sizes, look to see how much it would cost to get smaller rings for the Sora. It is bound to be cheaper that replacing the whole assembly. I also live in Seattle and I do just fine with 30/42/52 rings and a 11-32 cluster.
For around-town and light touring duty, I doubt you will detect any difference in performance or weight by going to the 105.
Regarding ebay auctions, the final selling price is not determined until the last second of the auction. This is especially true for high interest items. Shimano 105 stuff gets a fair amount of interest so I will just about guarantee you that the buying price will be set in the last minutes or seconds of the auction. The best way to see what items like that go for is to search completed items and see what the range of final prices is.
That sounds like good advice. The front crank is one of the more durable, long-lasting of all the moving components, so I doubt it would be worth it for now to shell out $100+ for a new crankset, deraullier, and bottom bracket. The front cranks aren't going to just give-out suddenly, they'll wore out over time.