I would try and budget in a few days to see some of the sites in the PNW( if your here in the summer time). Crater Lake, Mt. St Hellens and Mt. Rainier. I hear the rain forrests ni the Olympic mountains are great too. ( can you tell I like the Mountains?)
I can't go on your trip. But If you happen to be near me in Washington For a few days, and I have the day off. I wouldnet mind hearing about your trip over lunch or something like that.
+1. I did Cascades Park Road on my 550 (the only road that actually crosses into Cascades Park proper). It was amazing. I did Cascades, Olympic, Rainier, St. Helens, Crater Lake, northern PCH... all that stuff. I know especially for foreigners there is an allure to Route 66, but truthfully it's largely unscenic. You have to cross that part of the country somehow so I wouldn't say avoid it, but if you make Route 66 your only stateside destination you may be dissapointed. I would at least head north in Albuquerque to Santa Fe, then do the Million Dollar highway in western CO, then cut through Utah on hwy. 12 to Bryce/Zion, then south to Gand Canyon.
I've gotten to the point where I don't even ride old '66 anymore; I catch rides in Uhaul trucks on Craigslist and skip straight to Santa Fe or California.
Also, depending on your riding style 125 could be too little/way too much. If you'll be camping you can do it for much less. Hotels in the states range from $50 - $150. National Parks pass is $80 and pays for itself after just a couple parks. National Forrest camping is free - $8 or so if you use their maintained sites.