I make heavy use of D/(R+A), E/(R+A) (E=End), and D/E when I'm putting a build together. My priority on power selection - particularly before level 30 - is almost entirely dependent on how much damage each power does per cycle with no slotting.
Before about level 30, I'm usually working on building up my defensive and utility powers (i.e. travel powers, Fitness pool), so I don't necessarily have enough attack powers to keep firing off without interruption. At those levels, if I'm not looking at D/(R+A) I'm left wondering either how long I have to wait for my next attack to recharge before I can attack again or why my fastest cycling attacks don't seem to be doing enough damage to take anything out. And if I'm relying entirely on whichever power does the most damage, I'm also sucking wind before the fight is over.
Case in point, my Inv/Energy Tanker only had Barrage, Energy Punch, and Bone Smasher to work with from level 6 to level 24 when I added Whirling Hands. My next attack didn't come until 30 when I picked up Stun.
My Ninja/Force Field Mastermind only had Force Bolt and Air Superiority to work with as direct attacks. D/A doesn't help much at all there.
After I have my utility set behind me and start picking up more attacks, I can start thinking about sustained bursts of damage instead of individual DoT. But until that point, D/A isn't very useful to me. And if I could only pick one or the other, D/(R+A) is much harder to keep track of since R is variable according to slotting.
Now, don't get me wrong. I do think it would be useful to add viewing powers by (Damage)/(Activation Time) to the options in the Power Graph window. I'm just saying that tracking D/(R+A)
is useful.
What it sounds like you'd really find more useful, however, is a built-in attack chain planner like SherkSilver's old planner had. But that's an entirely different utility that would have to be added, which is much more complicated.