As I've said a thousand times I think all there is to "being existent" is to be an entity quantified over in our best scientific theories.

The point of Quinean Platonism is to inflate the formal criterion of quantification into an ontological claim of existence, not to deflate existence into a mere formalism.

So in this case treating abstract objects as being existent requires scientists to literally do nothing different.

It requries them to ignore part of the informal interpretation of a theory.

Neither nominalism nor platonism make predictions.

Then one of them is unnecessarily complicated as an ontology. You see to think Platonism isn't ontology. I have no idea what your would then think it is.

there are no nominalist scientific theories.

Whether theories are nominalist, or whatever, depends on how you read them. They don't have their own interpretation built-in, as I have pointed out a 1000 times.

I don't agree that the Quinean approach leaves out the semantics of physics a

nd I don't see how including the semantics would let you have a simple scientific theory that didn't reference abstract objects.

Theories can include numbers and centers of gravity, and reference them in that sense, and that is not the slightest argument for Platonism. Platonism requires that certain symbols have real referents -- whichis another sense of "reference".

Looking at a symbol on a piece of paper doesn't tell you that the symbol has a real referent. Non-Platonism isnt the claim that such symbols need to be deleted, it is an interpretation whereby some symbols get reified -- have real world referents --and others don't. Platonism is not the claim that there are abstract symbols in formalisms, it is an ontological claim about what exists.