Making ECDSA public keys one bit shorter
I think your question can be reduced to the question whether there is a significant subset of weak public/private key pairs in any of the EC groups you mention. I am not aware of any such weakness, but if it exists, it would put a large dent in the security of Elliptic Curve Cryptography as a whole.

If there is no significant risk you will get a key pair with less than the expected security, if you generate it uniformly at random in accordance with the relevant standard, but without discarding key pairs that have a public key with unwanted properties, the risk will still be insignificant even if you discard on average every other randomly selected key pair based solely on properties of the public key. It is important to reiterate that this argument only holds if you do not modify the private key generation in any way, but only discard key pairs based solely on properties of the public key.

This argument is based on pure logic. If you get the expected security from each of 1000 uniformly generated key pairs, and the adversary sees the public key of each one of them, you get the expected security from each ~500 of those that have a public key with the property you want. If the latter had been false, clearly the former couldn't be true either. Reduction ad absurdum.