You have other things to consider. But first, what makes you think it's
running rich? You don't say.

Replacing the plugs, rotor, etc. will never cure a running rich problem.
Shops do this because it's the easiest thing they can imagine besides giving
it a tire polish. Puts money in the till, but not much more. Careful--next
they'll want to replace the ECU, another easy one that almost never solves
any problems.

What you should really be paying for is a mechanic with diagnostic abilities.