Precision Spacers - Why?
Let's say your spacers have a tiny taper of .0005" (a half a thou) which is about 13u (microns - thousandth of a millimeter)
It sounds like almost nothing, but.....
Probably the sawblades have a similar tiny taper...,
How much (axial) run-out will you be adding to your setup?
Naturally it depends on how many saws and spacers are in a setup.
Axial Run-out Added by Tiny Taper (.0005" - 13u)
That "reasonably common bad case" is what you have to design around!
So buy good spacers...., keep them in tip-top condition....,
... and when they rust, or get dinged up, careful honing with emory cloth goes only so far. Then you need professional repair (lapping.)