Netherlands + Rhine or Belgium or both?

Looks like you've really only got about 8 days, not counting days when you're arriving from the US or departing. I'll be the first to chime in and say I think you should scale back and focus on fewer places. Your planned itinerary only has 1 or 2 days when you're not zooming from one place to another. Sure, things are fairly close together and train travel is efficient there, but it's just not realistic to spend every day checking out of your hotel, zooming off to another place, finding your hotel, checking in, getting oriented, and seeing that place before moving on the next day. Unless all you want to do is spend time coming and going.

I'd pick no more than 3 places, Amsterdam + 2 others max. I'd also skip the Rhine since it requires more time to get to/from rather than other cities in Holland or Belgium. I'd probably do Amsterdam + Bruges + (pick one more).

The main reason I'd give for going to Belgium is that the food, beer, and chocolate are to die for. Seriously. I'd fly there any day of the week just to eat. So, to me, it seems like a crime to be that close to Belgium and not go, if only for the food. The saying goes that the Belgians eat as well as the French and as much as the Germans. Sounds good, right?

"I'm also considering Limburg - Maastricht." Wow, that's an absolute first, someone else on this forum not only knows of Limburg's existence, but is even considering including it in their trip! Gotta go to work now, will finish this post later...

I would not miss Bruges. Rothenburg and Bruges are my favorite cities. I think you need to factor it in.

Day 8: Travel to Bacharach

This certainly doesn't take all day.

Day 10: Day trip to Burg Eltz on the Mosel River.

This certainly doesn't take all day

I would turn your days 8, 9 & 10 into just two days and then add Brugges for one day. I'm not familiar with the rural Neth. sites but I would be tempted to simplify things by omitting much of that and spending more time in Amsterdam, unless you have already been there before.

OK, back. Here are some random observations... I agree with the other poster. The trip to the Rhineland is longer than it would appear on a map. Not certain if you were planning to drive or go by train, but either way, Rotterdam to Bacharach would take most of a single day. Likewise, going back to Utrecht would consume nearly the better part of a day.

I then noticed how busy your first day is. Flying in from the West Coast, jetlag is going to smack you pretty hard. By the time you get to Den Haag, you will likely be exhausted.

Visiting both Utrecht and Haarlem is a bit redundant. I personally prefer Utrecht because of the livelier atmosphere. Utrecht is a much larger city, but the centers of both towns have much the same feel.

OK, Limburg province in Belgium. In my opinion, the overlooked gem here is open-air museum at Bokrijk, near Genk. It features reconstructed period houses and municipal buildings from throughout the Flemish region of Belgium.

My favorite town in Limburg is Hasselt. Not a tourist mecca by any means, but a very pleasent 18th century city. If you like genever, there is a museum and tourable distillery. If you're into high fashion, for some reason this rather small city competes with Antwerp as the fashion capital of the Dutch-speaking world. For kids, Plopsaland is an indoor amusement park based on a popular Belgian TV program. Finally, if you visit in the winter, the Christmas market/carnival here is the most elaborate I have seen in Europe.

Finally, Maastricht is also a very pleasent city, but no real sites. If you end up in either Haarlem or Utrecht, visiting here would be redundant.