Maybe your shop meant "thrust alignment" when they said "4 wheel alignment".

A thrust alignment is really a front wheel alignment, but what it does is align the front wheels exactly in relation to the non-adjustable rears.

A non-thrust, front wheel alignment adjusts the front wheels in relation to the center line of the car. If the rears are perfectly centered and otherwise correctly oriented to the car's center line, then there is no need for a thrust alignment. But if such is not the case, then the thrust alignment will result in a car that tracks better and wears the tires less.

If your car has ever been hit at all, then I would definitely choose the thrust alignment. Even if it has not, various factors can cause the rears to be slightly out of kilter with the center line.

I think the few extra $$ for a thrust alignmnet is well spent.
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'84 '285' rice-eater with lotsa hp & performance goodies & an 8-legged tenant