One of my trip ideas is to fly into Seattle, circle Olympic Park, then go through Victoria and Vancouver in a week. Doable or no?
Definitely doable: I followed an itinerary somewhat similar to this (but not including Victoria) in summer 2003 over less than a week. However, my visit to Olympic National Park was rather abbreviated. The Hoh Rain Forest is one of the rainiest places in North America, so I don't recommend it for camping unless you are prepared to deal with copious amounts of rain.
What are the logistics of visiting the peace arch? I've seen pictures of people walking through it, but the information I've been able to dig up seems that you're not allowed to do it, and in fact there's no parking nearby for people that might want to. Wikipedia implies that in order to cross the border on foot you have to "be cleared by the country you want to enter". But how does one do that, drive through and be cleared by US customs, then park and double back?
My experience of the Peace Arch dates to 1991, so things may have changed, but at the time the most convenient way to visit the park was while waiting in queue at the border crossing. I don't think September 11 has changed things that much. The problem is not getting to the park, but rather leaving, which you must do through the Customs checkpoint of the country you are entering.
I have never had a desire to do a repeat Peace Arch visit because of the waits at that particular border crossing. In 2003 I was in the Fraser Valley and wanted to go to Seattle (almost due south), but drove a considerable distance out of my way and crossed at Osoyoos, which is as close as Canada comes to high desert, and took the North Cascades Highway (SR 20, very scenic) back to the vicinity of Seattle. It might be closed in November, however (Wikipedia gives the median closure date as 26 November and the median open date as 20 April).