My wife's old bike (Trek 1.2 Al+CF fork) has 25mm tires on the front mounted on a standard 18mm rim.

I've tried running lower pressure in front (~80 psi instead of ~90-100). It did make a noticable improvement in the ride quality, but it also resulted in a much squishier handling bike. Under aggressive braking and handling the tire wanted to squirm more. Upping the pressure improved things, but at that point you aren't seeing the ride quality advantages. I'm guessing a wider rim would make things better.

About the brake opening thing, I suspect its a combination of tire & brake setup. I like my brake pads running close to the rim. When I open the quick release it doesn't clear by 1-2mm. If you run wider brakes you won't have an issue.