Glad you enjoyed it.
It would all be just as accessible to Americans as Europeans. You are not likely to get hassled any more than Brits are.
For some reason, Americans are pretty worried about venturing into this part of the world ... (at least 90% of the bike travellers in this part of the world are European - with a handful of Aussies and Kiwis and Americans making up the remaining 10%) ... but I can tell you its unjustified. If you talk to some of the few Americans ADV guys that do venture into this part of the world, like:
or Beta (http://www.advrider.com/forums/showthread.php?t=652622
or Sherri Jo Wilkins (http://sherrijosbecauseicanworldtour...max-results=50
or the current ride report from RoninMoto (http://www.advrider.com/forums/showthread.php?t=781893
or the very clever and entertainingly philosophical (and soon to be resumed) blog from Genghis9021 (http://www.littletinyplanet.com/wordpress/?page_id=953
you will find they will probably all tell you they love it and the people are, as a general rule, great, and much better than they had expected - most of those folks were travelling solo too.
Officials, like border guys, will treat you the same as they treat Europeans ... In fact Americans are treated better than Brits technically. Americans can now get 3 year multi entry tourist visas for Russia. Brits can get a maximum of one year - and only for a business visa. (French and Germans can get 5 year business visas). Brits (and other Europeans) need a visa for Mongolia. Americans do not - you can just show up at that border. As for Russia, when you apply for a multi entry visa, you get thoroughly vetted by the FSB (former KGB) before you even get issued an invite to apply for the visa. So to get a multi entry visa it means you have already been "approved" by FSB head office. The small fry at the border are not going to overrule your approval by head office. I actually have never heard of any bike traveller with a visa ever being turned away at the border.
Once inside Russia, there are only two distinctions - Russian or Non-Russian. What type of non-Russian you are doesn't come into it. Restricted areas are the same for Russians and Non-Russians ... the main difference is that Russians can get permits to enter restricted areas much more easily than non Russians. In any case, I have routed the Sibirsky Extreme Trail around any restricted areas - so no permits needed.
Kazakhstan is not going to hassle an American, unless you are a rabid democracy activist. Their traffic cops hassle everyone equally, Locals, Europeans, Americans.
A good mate of mine is an American adv rider living in Moscow ... I will ask him to add his perspective.