I broadly agree with the last post.
Visibility is an issue, and to some degree we rely on lookout and the big sky theory.
If I can be a little contentious, I think being in touch with an ATC unit in the open FIR on a basic service gives a false sense of security if you're relying on it for traffic avoidance. Many is the time that I've been told about one piece of traffic but not the other five or six. It works if there are very few people around - but on a busy day I think it's largely useless. And to be fair to ATC, that's not what they're contracted to do on a basic service. I don't think it's very useful to change your route just because you're told there's something in your path - the likelihood is that you'll just be conflicting with something else.
I think there are only two solutions, other than the Mk 1 eyeball.
1. Ensure that fewer people fly and provide a deconfliction or traffic service. Usually known as CAS.
2. Or technology - but the costs are pretty high, and the cost / benefit perhaps doubtful, particularly if it's regulated technology. There's a reason transponders and TCAS etc are much more expensive than Flarm - it's all designed for the CAT world.
Full Wings' point about different people wanting very different avoidance standards is a good one.
Paul