Jeppe,
I'm late to this discussion, and have only skimmed some of the replies, but I think it is imperative that someone point this out if no one has yet. As one who has ridden European trains as well as Amtrak, please be aware that American trains are not at all like European trains! :huh: Please don't expect a similar experience.
My experience with European trains is that they routinely function like a well oiled machine. Ours often do not.
Except perhaps in the northeast corridor (New York--Washington, DC for example), American trains are not as frequent or dependable as European trains. In fact, some people consider the long distance trains more like a type of land cruise experience (but not a luxurious one) rather than pure transportation. This is not necessarily a negative, and is NOT meant to discourage you; I absolutely love traveling on Amtrak! But please be prepared for possible delays and poor on-time performance, equipment malfunctions, and varying degrees of on-board service ranging from excellent to nonexistent to obnoxious. Hopefully you will experience good service, as we usually have, but it does vary quite a lot.
The reasons for the differences between European and American trains are many, and are not necessary for discussion in this thread. Just be aware that American trains are very different from those with which you are familiar. Having a laid back, go with the flow attitude and a spirit of adventure for just enjoying the ride will be very helpful in making your experience a pleasant one. Again, I'm not trying to be negative toward our American trains, but having realistic expectations is important.
I've not ridden many of the suggested routes, but in general I agree with the posters who suggest a fairly simple itinerary, especially without access to a car. As for places to see, Washington, DC is a city with many attractions and much history, and the Pacific coastline is beautiful. The Grand Canyon is certainly worthy of a visit if you can make it fit into your itinerary. I have not seen the Rockies (except from a jet) but would like to. No matter the routes chosen, I wish you both a pleasant, memorable trip.
One final note, of which you are undoubtedly already aware. Obviously a coast to coast rail trip involves great distances. An upgrade (if that is allowed on a pass?) to a sleeper for at least part of the trip might be worth the cost, especially if layovers are short. With a sleeper, all meals in the dining car for both passengers are included in the fare, which makes the cost not quite as daunting. (Two basic fares, one accommodation charge.) OTOH, many here on the forum travel in coach for long distances and do fine with it.
If you decide against a rail pass, amsnag.net is a great resource for finding the lowest available fares.
Best to you both, and happy travels!