Me. Long time Campy guy. My opinion is, the UT is far superior to old square taper. Now did square taper get us down the road just fine?
Yup...but perhaps more reports of square taper BB's failing compared to UT. I love my UT carbon Chorus compact. One of the best products Campy has made IMHO. Some run this crank on other gruppos in fact it is so good. I believe it is stiffer as well but the biggest thing is set up.
It is much easier to set up compared to square taper. You may know that square taper crank arms were hugely sensitive to bolt torque affecting depth of arm draw onto the spindle due to the drafted square. Ultra Torque Hirth joint is line to line...torque it to spec and forget it...easy to get apart and service. I have had no problems with contamination ingress...but....I am a fair weather rider on my road bike (not mtb).
Don't even think about square taper unless you have one laying around and don't want to buy a crankset.
As to facing the BB...most new frames today in my experience come pre-faced. My Look frame didn't require to be faced and the threads were clean and chased as well.
Campy has just redesigned their cranks again a la Shimano's separate splined left crank arm solid axle design which is no doubt excellent as well although Campy still offers the Hirth saw tooth joint on certain models.
Hope that helps.