Bottom line: there aren't only false negatives (robots that successfully masquerade as humans). There are also false positives (humans that are mistaken for robots). This obviously takes us into ymmv territory. Personally I would rather let in a few unwanted robots than lock out a few honest humans. Unless they're from China or something, duh ;)
I've got the header logs running at the art studio's site. Haven't collected enough information to do anything about it* but do note with interest that the Yandexbot sends an accept-language header. Wonder why?
What does Wsip mean? It showed up at the end of a DomainTools query with an attached IP that was different from the first one. It may even be the site's own IP-- it belongs to my host-- but the site doesn't have a fixed IP so I can't be sure. I got as far as "Web service initiation protocol" and then the explanations lapsed into Hungarian.**
* As noted elsewhere, this site is smaller than mine by a number of orders of magnitude that would seem to be mathematically impossible.
** As in "It's all Hungarian to me".