Car is at 200,000 and I feel a difference in the way it runs, it doesn't accelerate smoothly or switch gears smoothly even though its an automatic and even when I brake my car is rocking back an forth on the way to a stop. What seems to be my problem, should I just change the spark plugs?

when you break does the steering wheel shake alittle back and foward?if it does sounds like you need new breake pads and break rotors

get an alignment. you might need ball joins and outer tie rods. as far as acceleration, change the plugs and wires, replace your o2 sensor, oil change, change the transmission fluid or see if it is low because that would be the cause of hard shifting. your engine mounts might have gone as bad as well.

How much is the sparkplugs and the wires worth ?? By wires you mean the one that connects to the plugs right?

Spark plugs should be about $10, not sure about the wires since I've never bought any, and yes, the wires that go from the distributor to the spark plugs

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People(like myself) recommends "NGK" spark plugs and wires for high quality but the autozone ones are much cheaper and gets the same job done with a CHEAPER drive.

your problem can be anything, i suggest, specifying particular symptoms, where its coming, etc.

Could be 1 single thing, like it could be many things causing all this.

I would say give your car a nice tune up (Engine oil, tranny oil, air filter check, fuel filter, spark plugs and wires, distributor..) Also maybe your engine mount(s) could be shot and causing things to be not a smooth as they should.
It can affect the acceleration (like i believe it does on mine), and changing gear might not be as smooth either (for man. trannies).

Otherwise you should make it inspected by a mecanic or give us more specific details.