Brake replacement

I have a 1993 Mazda B2600i with 180000 miles. I'm starting to replace the front and rear brakes. I am trying to find out if I should replace the wheel cylinder on the rear and/or the calipers on the front even if there is no sign of leakage. Also should the return springs be replaced.
I read on one repair site where the person advised replacing the cylinder when changing the drums and shoes as the new parts will be thicker and drive the inner parts of the wheel cyclinder back to the middle where there is probably dust and other junk that would cause problems down the road (leaking I believe is what he said).
I have also seen where vehicles with high mileage shouldn't replace the brake fluid because of worn parts not moving correctly with all new fluid. The brake fluid should only be topped off. Is this correct?
I want to do this right the first time and not have any reason to take it to a shop (cost almost more than the vehicle is worth).
Thank you,

Jeff