spark plugs question

hey guys i was just wondering whether or not changing your spark plugs is supposed to make a difference or not. i put in my denso iridiums on monday. so far i have noticed it seems to run a little bit better but i was wondering if i should buy new spark plug wires too?? i realize i'm not really gonna gain like 10 hp or anything, but just in general will my car be running better with new wires too??