Is it important to change cap rotor and plug wires?

It is difficult to believe your claim. Have you personally owned the car for the entire 18 years? Why do you even think the parts are original??

Plug wires, I could *maybe* see - if they were high-quality silicone, especially. But it's HIGHLY unlikely - if not outright impossible - for at least the rotor to not have carboned up from arcing during that length of time. Even if so, the parts DEFINITELY need replacing by now.

However, you failed to provide any relevant information regarding MAKE, MODEL, and ENGINE, so it's also impossible to give you any kind of accurate estimate on replacement cost. Could be under $100 for cheapo parts for a SBC, to $500+ for OEM parts for a Mercedes.

Yes, it's time to replace those. It own't run better if they are still in good shape, but at 250K miles, they are about worn out. Replace the spark plugs at the same time.

My last one was about 85 bucks for parts and I did the work myself, so around 200 bucks if you have a shop do it, less if it's a 4 cylinder. You can call around for quotes. Any competent mechanic can do the work.

If they need changing you will notice, they don't really go bad until they stop working.

do a proper service instead, start with an oil change, cam belt (if it's long since it was changed last), a new air filter and maybe a clean fuel filter. if it's a injection car you might wanna have the injectors cleaned.

u are way past due for a tune up

Need to know what year,make,and modle car you have.