Why don't you use a case?
Do you dislike them for some reason?
A few reasons…
• I prefer the tactile feel and the natural look of the phone/device itself. That's what I bought it for, not the feel and look of a case.
• I have seen few cases where the design is as good as or trumps the design of the iPhone itself.
• I don't like something in between me and the phone/device. Even with ultra slim cases there is added bulk and some make it harder to use the touchscreen. I don't like cases that fold over the screen because I have to open them to actually use my phone/device.
• I don't like the expense of more premium cases, but lower cost cases offer less protection and stand up less to wear and tear.
• Some, but not all, cases allow for debris, dust and other foreign particles to get in between the device and the case. That can make the case look grungy and actually damage the device.
• Case maintenance was not in the original plan of buying the device/phone.
• Cases tend to prevent that 'patina' you mentioned earlier. I don't care for dents, bangs, scrapes, bends, cracks or any other damage like that but to my mind a phone that has some of this 'patina' is a perfect example of a seasoned tool. Finally, that patina is mine. Only my device has that and it's unique to me.
There are some awesome cases out there that either look great or can minimize all this, but they are still a case and stand inbetween me and the device.