I do replace them when I the outside shows cracks.
In case for the Mac Plus Analog board: the Kemet AC filter/surpression capacitors of 4700pf and 470nf definately need to be replaced as on all my 8 Analog boards their box was severaly cracked.
I agree not to replace them as long as they are still within specs ( even Ceramic capacitors can go out of specs badly ) and if they pass visual inspection.