You can get new housings from the dealer for $35 or so, for the factory case or $15 or so on ebay for a
case from China. I have gotten both and prefer the OE cases, which fit together better and have better feel. The Chinese cases tend to be too hard. Oh, and the cases do NOT come with new Porsche crests. If you want a new one, you need to buy those separately.
With a new case, switches and a battery your keys will be as new. There is no real reason to buy a new remote in 90+% of cases in my experience. Do note that if you replace the case you need to transfer the immobilizer transponder pill and key to the new housing. This is pretty easy. Also note that you need to start with a key and remote that was programmed to your car. If you need another remote, the only way to get a new one with the tag that has the programming code.
I bought a bunch of the internal switches a while ago with the idea of putting this type of kit, but never got around to it as is the case with a lot of these types of projects...