Yup, same, I wear jeans at all of them.
Our DC and our chief are insane about appearance of uniforms and gig-lines, all 'volun-told' events in suits, etc.
The parks only have one signature - Le Cellier - and being how long their walk-up is and the ADR availability, they'd likely still fill out.
The resort signatures would definitely fill with an enforced dress code. After the Dis arguments about dress, I made it a point to actually pay attention last trip at the signatures each night and the vast majority are dressed according to the code. It could be because we go later in the evening, not sure.
As for the server, they shouldn't account for dress to an extent of their service being different to the point it impacts the guests' experience. But at the high-end places we frequent, I've noticed far better service when I dress to their code. It's the same with the NYC taxi experiment that focused on dress and appearance- the nicer dressed individuals yielded cabs substantially more than the latter, to the point cabbies even passed the other individual and picked up the well dressed.
The thing with Disney and restaurants is the existence of a dining plan. With the plan, a lot of people tend to 'go all out' on their trip and this includes dining out how they don't dine out at home. You'll notice the non-dining plan locations at Disney have consistently better reviews than those who are on the dining plan. Why? Disney knows, the restaurant owners know. There's a reason why you don't see park attire and out of control children at Shula's and BlueZoo, but see a fair share at Yachtsman or Flying Fish - those in tank tops and park clothes usually don't go upscale back home. Servers always assess the diners and see what type of night they're going to have at work, from their appearance to their demeanor. The dining plan isn't an issue when the guest is dressed presentably, but if you're in park attire at Narcoossee's on the dining plan, I'm already thinking my tip is going to lack as compared to the table OOP or on plan, dressed to the code.