Have you ever smoked? I feel like I only hear this sentiment from people that have never tried nicotine.

Nicotine absolutely produces effects that people enjoy. Smokers don't just do it because they want to smell bad and look cool.

Is there proof that the positive effects are still there after you're hooked? Or are the "positive effects" at that point just a cessation of the negative effects of withdrawal?

Yes, absolutely. It's a stimulant, similar to caffeine. Just like how nearly everyone adjusts their caffeine consumption based on the situation (got to buckle down, drink an extra cup of coffee), people do the same with nicotine. It also still works as an appetite suppressant.

Now, the euphoric effects that you get at first, those very rapidly go away with tolerance. With habitual use, you probably only experience a tiny shadow of that with the first hit of the day, or a respectable replay if for whatever reason you go a couple days without (which is heightened by the cessation of withdrawal). The nausea and disorientation also go away, which is nice since otherwise it would be a problem.

We need objective research into subjective effects to really say either way, but such things to me are worth knowing

Yes, I smoked for a decade. The only noticeable effect it produces after a while is providing relief from nicotine withdrawal symptoms. It does feel similar to regaining focus or calming your nerves, so smokers trick themselves into thinking that's what it actually does. Nicotine is also way, way more addictive than alcohol. I've gone months without alcohol with almost no mental effort but day 3 of quitting smoking was probably one of the most miserable and challenging of my life.