not sure what you consider a tune-up. Cap, rotor, points and condenser is what i consider a minor tune-up. Plugs and air cleaner are next on the list followed by wires and fuel filter. Timing can also make the car run rough. Vacume can also cause problems normally highlighted by a fast idle.
A bad cap, rotor or points can make the whole engine run bad, where plugs, cap or wires can attack a single cylinder.
If it has been 20,000 i'de probably get everything. If the wires are looking real good skip them. With a clogged fuel filter the car will idle good but run bad under load and acceleration.
Good luck
Motor