Nemo wrote:One of trail O's problems, if it is to be a serious 'sport', is its inherent intellectual limitations....[etc]
Now there I definitely part company with Nemo! Whilst there may only be one right answer, you've got to find it, and find it many times. On top of that, you don't have unlimited time: many competitions have been decided on the timed controls, and if (as I think Kedge suggested) elite Trail-O goes down the route of timing all or most controls, then the pressure really will be on! I don't think there is anything lacking in the mental demands of trail-O - indeed in many respects it can be tougher!
The fact is that there are many activities that are far less intellectually/technically demanding than Trail-O. One could argue that this can include a lot of MTB-O and Ski-O - after all they rely primarily on route choice rather than fine navigation. As an earlier Guest suggested, foot-O on easier terrain may come into this category too.