All a dimmer is going to do is dial down your wattage, you will still be depending on whatever temp sensor you have now. This means if you have temp swings, you will still have them and just have less wattage and less heat. The pid actually controls heat in the pit. On an electric you can set a PID for any temp that your element can attain from 1* above room temp to full on heat and it will hold it with a degree or so with precision.
If you are trying to smoke at a lower temp, the dimmer will let you, but you will still have temp swings. But if you are just wanting to control the heat, go PID.
As to the cycling, no it will not hurt the element. In fact soft pulsing is easier on an heating element that hard switching. What wears out are analog relays which is why PID controllers use SSR's instead. No moving parts at all.