In my experience, if you are wearing racing gloves, alcantara gives better grip on the wheel than leather. With gloves on, leather wheels always felt really slippery to me. I always thought that was why they typically wrapped racing wheels in alcantara, but not sure. Without gloves, it was the opposite and leather seems to give more grip, at least in my experience. Maybe alcantara is better if brand new. Rubber works better than both, gloves or not, but probably wouldn't fly in a car like the Emira.
Alcantara would probably make for more grippy seats, at least if you are wearing clothes

A real racing seat with straight side bolstering is going to be significantly better, regardless of the covering though and is highly recommend if you plan on doing a decent amount of track work. Actually not as bad as you might think for a daily driver. If it's well fitted, they are really comfortable, just harder to get in and out of.