I would consider myself to be an experienced lifter both raw and geared. I am 26 and have powerlifted since I was 14 so I am not new to this and am past making newby gains. I have ran 5/3/1 since January and had great gains. I ran it exactly as planned for the first cycle but changed it slightly to meet my individual needs the next 3 cycles. I changed it so that I don't deload all lifts in one week.
My deloads are staggered with squat being week 1, bench week 2, deadlift week 3, and OH press week 4. For instance on week 1 I would deload squat, 5's on bench, 3's on deads, and 5/3/1 on overhead pressing. Week 2 would be 5's on squat, 3's on bench, 5/3/1 on deads, and deload on overhead pressing. At first it was strange but once you have done the cycle it works great. In preparation for an actual powerlifiting meet I changed it even further to throwing in some heavier singles.
It is true that you have gains in the beginning and they taper off later but isn't that true of any program? Wendler outlines in his book what to do when this happens. After the competition I will most likely continue some aspects of 5/3/1 because I had great success with it.