It's a nice idea and would definitely help reduce the wear on the already craptastic D-Pad on the 360 controller, but I don't think it's too necessary. I've had no issues going back/forth (same goes for LS mates who use a pad) on the bars aside from the occasional game hiccup where Up/Down won't switch bar levels.
If I need to pull off an ability ASAP, I just move one of my fingers about 2 inches from the trigger on the gamepad to the number key on my keyboard. Though this is a very rare thing for me to do seeing as combat isn't quite as fast-paced as some people make it out to be.