To answer the OP, I don't think Spyderco's knives are overpriced. There are some that are more expensive than I'm willing to pay, but that doesn't mean they're overpriced. Just that I'm not interested enough in the knife to fork over the money. Value is a different subject entirely, as value is dependent on the price to performance ratio. Higher quality materials may cost a lot more, but only perform a little bit better.
Addressing the reason behind manufacturing in Taiwan vs. the US. There are a few reasons. Before the Sage model came out, very few of Spyderco's knives were made in Taiwan. If I remember correctly, back when Sal was shopping the Sage idea around, he met with lots of knife makers, many of them in the US. The Sage was an ambitious project, with one handle size and shape accommodating various lock mechanisms. It was a huge engineering challenge as every variation would have to be re-engineered to make the project possible. There were a few makers that were capable of the quality that Spyderco demands, but the Taiwan maker was the only one who was both able and WILLING to take on the project. The Sage was a success and naturally all the other Sage models would be made there.
Now this next part is speculation, but based on economic realities (and little bits of info that I've gleaned from posts here and there by Sal). The Sage was released in 2008, the very same year that the economic crisis hit. Part of the fallout of this crisis is that businesses started playing it safe, not expanding, as new buildings and machinery are expensive, they had no idea how future business would be affected by the economy, and it was a bad time to borrow money. Concurrent with the depression/recovery years, Spyderco continued introducing new models and while also becoming more popular. As popularity and sales increased, the Golden plant couldn't handle all the demand with their current capacity, but expanding at that time was still too risky of a venture. Taiwan had done an excellent job with the Sage, had a good working relationship with Spyderco, and -very importantly- had the manufacturing capacity and skill to take on more models. So in that economic climate, it made sense to hedge bets by offloading work rather than taking on the economic risk of expansion, as their is a very real risk of expanding too much or too quickly. Fast forward a couple years and things are currently looking good with Spyderco. Golden capacity is maxed out and they decided to expand their plant, which they are currently doing. But this takes time; they have to build the buildings, train the workers, and the lead time on some large specialty equipment can be years.
The good news for those that want to buy domestically is that Golden will be producing more in the near future. Expansion is underway and I recall Sal saying they have been training new employees (IIRC, it takes a good 6 months). I understand the desire to buy American and, while I choose to buy the Taiwan models I like, am fine that others choose not to.