Just bear in mind that although the T500 does work on the PS4 it isn't officially supported and is lacking the options/share buttons.
The current best wheel that works on a PS4 is a Thrustmaster T300, but things start to get very expensive if you want a gear shifter and 3-pedal set-up for the proper sim experience.
Looking forward, if you want a wheel that will work with the PS4 too, then you are better off waiting a while until there are more options available.
Does the wheel change things?.... Yes and no.

On SS tyres, the gain in lap times is really tiny, I could match my lap times on a pad. but here's the thing, since I purchased the steering wheel I have only used the pad once to play GT6. The wheel gives an overall nicer experience and is more fun/challenging.
Please don't expect to buy a wheel and be as quick as you are with a pad. The wheel takes time to learn and regardless of what anyone may say, it isn't 'lifelike' it's meerly an input device and it won't feel like driving a proper car. It will take you probably 2 weeks to get decent with using a wheel, to begin with you will spin rwd cars and become frustrated, but you need to be gentle and stick with it.
Tuning can be different with the wheel. At least on GT6 it is.
So, yes, get a wheel, but possibly wait a while first and see what happens with the PS4 compatibility.