Definitely worth trying especially stacking them up, it's sort of a poor man's super sucker.

Mine picked up around 18hp with the right spacer combo, back when I had a street dominator 383 intake. But that was 3" worth of spacers which told me the manifold was lacking something.

The victor 383 intake was better to begin with and it only picked up 7hp with the addition of an open spacer.....
a 4 hole spacer did absolutely nothing. It did not even change A/F ratio noticeably.

It's worth testing at somewhere like Jake's, so you can catch the little changes (ya know, 7, 8HP or whatever) when you come across em. It ain't much but if you got it, keep it! Myself I would have a hard time seeing 7hp on a timeslip but I am really not that good....