nh2301, you are right: as you said: "although given my experiences with immigration, no guarantees!"
Even if my embassy told me that I do not need a visa, I would consider getting one.
What if the guy at immigration control thinks differently? You can be sure that he/she would not care about what the embassy said. And then, I haven't got direct experience, but, given the controls for US immigration, in the least of cases you will waste a lot of time, and I do not even want to think about the worst case....
I know, it sounds wrong but it's just a matter of weighing risk and cost.