I agree that there is a point of diminishing returns. The most important factors to me are visibility, both in very bright and very dark environments, ease of use, and roadworthyness (is that actually a word?)
While I certainly wouldn't go pay another $100+ to replace a +/- .1 cent with a +/- .02 cent tuner, I would (and did) to replace a Boss TU-2 that I couldn't see in sunlight. And if I were in the market for a new tuner, I would certainly go with the most accurate that fits my other requirements.
The Sonic Research ST-200 that I have is built like a tank. Also, the Sonic Research is a true strobe, not just an LCD virtual strobe, and is the fastest tuner at recognizing and reacting to the played note. The new ST-300 series is supposed to be even faster and brighter.
Bill, tgo