Is the test for paraneoplastic antibodies clinically useful?

Very much so: Some of the most puzzling clinical syndromes are caused by the immune response to tumors that may not be known to be present yet. There's a group of antibodies for which we can now test that will rule the known syndromes in this category in or out. It's not cheap and isn't to be ordered lightly, but it's a standard part of health care.

Not much: I have not found this test of much use. Most times, it is a clinical diagnosis. The test for antibodies does not change much. It is just for academic value and it does add to the cost of care, unnecessarily.