Authentication really doesn't do anything that extending your id key by that number of bits wouldn't do, i.e. a 32 byte random ID is just as hard to collide as

Authentication really doesn't do anything that extending your id key by that number of bits wouldn't do, i.e. a 32 byte random ID is just as hard to collide as a 16 byte random ID and a 16 byte signature. Technically, if there are any weaknesses in your signature, they may end up making your ID+signature easier to collide. Just going with a pure random ID means 1 less key that you have to keep out of source control.