PoS coins use the number of coins held as the basis for their signalling system. Since coins have an exchange rate, they obviously do not fulfill the criteria of having no value, either practical or intellectual. Thus PoS is not an viable mechanism for honest signalling.
The criterion of having no value is a theoretically sound one for proof of work systems. I am not convinced it's correct to apply this criterion to proof of stake systems the way you did it, because PoS and PoW solve the distributed consensus problem in a different manner. Let me try to explain:
What's the reason behind the criterion that the calculations in a PoW system must have no value (either practical or intellectual)? This simply to increase the cost for an outsider to successfully attack the system, right? To ensure that "telling the truth" is more profitable than "lying".
With PoS, the signalling system is indeed based on coins which have value. This means outsiders (those who don't own coins) can't influence the signalling system. The coins however only have value as long as the system functions as it should (the same is of course true for PoW systems). I therefore think this system also ensures that "telling the truth" (which makes the system functions as it should) is more profitable than "lying", and could thus be a viable mechanism for honest signalling.
The systemic incentives are opposite though. Where PoW encourages decentralization, PoS encourages centralization.