A lot of the roads where I live are similar to that described in the OP. I find the pragmatic approach is usually best.
If you are being approached by someone driving way too fast, or looks live they have every intention of blasting blast you without actually taking any evasion action, I'd ride assertively in the centre, to make it clear that I am expecting them to slow down. But I'd also be prepared for the possibility of taking massive evasive action myself in case they don't take the hint.
Different vehicles/situations require different responses. Most rural roads here have passing places that aren't desperately far apart, so pulling in and waiting for either party is usually a bit quicker than doing a shuffle-dance in the narrow section.
In the absence of passing places I'd still be pretty pragmatic. Sometimes the verge on one side is more solid than the other, do whatever is necessary to prevent either side getting stuck/wet feet/risking peril. I'm pretty tolerant of tractors towing trailers - it's often easier to get off and walk round a stationary one rather than risk being knocked in a tight space.
I always wave, unless they've been a total dick.