RTW ticket advice

Using one world or star alliance limits you to the routes their airlines fly. That's why you're having to back track.
Considering the continents you want to hit, you're going to be at the top of the mileage for either of those two so it may not be worth the savings.
I used star alliance to figure out our proposed route and had to make some adjustments (Toronto to Santiago, Sao Paolo to Jo'Burg, Egypt to London, London to St. Petersburg, Calcutta to Bangkok, Singapore to Tokyo, Tokyo to Toronto). That was $6500 (London legs not included).

I also looked at what those same flights would cost individually. Guess what? it was $1000 cheaper to buy them individually. And if we take the lowest fare instead we can save $2000.

Also look at airtreks.com? Their route planner not only gives you a ballpark of costs, it also suggests popular/available routes.

There is no mileage limit on the Oneworld Explorer ticket, only number of continents, no. of flights within each continent, and 20 flights overall (16 if ticketed after 1 June 2008.)

You could do your trip using a 5-continent Oneworld Explorer with a route something like this, starting in SF since Oneworld doesn't have any transpac flights from SEA -

San Francisco - Tokyo - Bangkok - Hong Kong, (train to Beijing and Moscow,) Moscow - Budapest - Cairo - London - Cape Town/Joburg (overland to Nairobi,) Nairobi - London - Buenos Aires - Rio - Santiago - NYC - SEA with a couple of extra stops here or there.

You'd have to do SA - Kenya in reverse order owing to some obscure but unavoidable rules in the ticket regarding transiting Europe to/from certain African destinations. You wouldn't be able to stop over in London on the way to South America - just change planes and be in Europe no more than 24 hours.

There are numerous riffs on this itinerary, of course, but it's certainly doable.

You also have the option of buying a one way ticket to Bangkok from seattle and maybe purchase your RTW ticket in Bangkok. We did the same thing two years ago on our RTW. We left from Seattle(Where we also live) and used frequet flier miles to get to Europe and Bought our RTW in London. It was 1200 dollars cheaper each than purchasing in the usa. We looked into airtreks and they couldn't come up with a better deal. We just skipped the last flight when we got back home to seattle. I have heard of many people getting there RTW ticket also in Bangkok. I dont know who they used but a little reasearch might find a travel agent there that could do it for you. Your trip is similar to ours as we also went to SEA and overland in Africa.

You will enjoy you trip. It will be the time of your life.

Any questions just pm me. What part of seattle are you in?
jeremy