I went through this same thought process as well.. Personally, I went for the 18-200.
For local use, I figured when you go out, you will know what lens you will use for the day and fit that single lens without having to change all day.. basically it's still lighter than having to carry multiple lenses out.
Buying the 55-210 still means I had to carry something else.. and if you look at the length, 55-210 doesn't save you much in space but just weight.
For travel, I just came back from Iceland with the lens, and find that the 18-200 isn't that heavy to me (I hand-carried it without strap most of the time, putting it into bag when not in use), and proved versatile in areas that I couldn't change lens (e.g. mist due to waterfall, beach side with sand and pebbles blowing, etc). I rarely used the 55-210 range but it was still worth carrying for those shots where I needed it.
As a side point, interestingly I found I took more videos than I expected and it was really useful for me in this regard. If you want video, having full range of zoom really helps a lot. I think this is the key aspect that will do it for you.. being able to zoom to someone's hand to see what they're holding from a distance, capture facial expressions clearly, and then zoom out to the event and environment, this is something you want to be able to do. 18-55 is alot more limited here, and you need to do more following to track your subject which results in a more choppy video.
As for 18-55, while it can fill in for days you want to leave the 18-200 home, it's noticably worse off in PQ than the 18-200 to my eye..
The 18-200 isn't the sharpest and has limitation in aperature, but sometimes I don't even bother switching to the CZ 24mm especially when using about f8.. composition is still more important than just abit more sharpness, and it's an acceptable compromise to me while I felt the 18-55 had quite abit too much trade-off for my liking.