Yes, I've been doing this for several years. I don't consider it a necessity, but a nice tweak. The exact amount isn't that critical, but I use about the amount you stated. The everclear lowers the viscosity/surface tension of the solution a bit and helps minimize brush marks and other irregularities. I find that it has very little effect on how quickly the solution is absorbed into the paper.
I brought home a gallon of the stuff from Montana last year, which is almost gone. I use quite a bit of it in the collodion process. That's my story and I'm sticking to it...
I don't do this, as I have had problems with uneven paper absorbtion with the addition of the alcohol. I think it may be somewhat dependant on humidity and paper choice.
Basically, I haven't found it necessary or beneficial to my working methods, and I don't believe there is any reason to complicate the process with a chemical if it is unnecessary to the process.