what's the secret to making a good robot in robocode

From the perspective of normal (relative to orbit direction) GFs, whan it comes down to is that you'd have is a movement which alternates between GF 0.5 and GF -0.5.

It's true like you say that this could have some level of effectiveness against targeting systems that are using firing waves only AND are missing certain segmentation dimensions...

I would say it could be 'exploiting' yes, but I would also guess there are very few targeting systems you'd reliably trick with this. It seems extremely fragile. Your maneuvers to "arrange to alternate orbiting ..." would give away which of GF 0.5 and GF -0.5 you're heading to in certain targeting segments/dimensions (easy near-100% hit rate against it), and even without that, asymmetry in the result of non-firing waves would cause a lean toward one or the other, causing an easy ~50% hit rate.

It would be interesting to see a demonstration of what in practice would be tricked by it though.