Depends on how you ride. At highway speeds (70 mph), the Empulse R claims 56 miles of range, vs the 43.5 miles the S ZF9 claims (29% better range from 18% more battery). Note that the base Empulse and the Empulse R may have different highway ranges if the Empulse R benefits from an aero fairing.
I do most of my riding between 45-55 mph, and I see a noticeable difference in range when I tuck in. I imagine an aero fairing would do much better. I get about 60-70 miles of range in my typical riding, I would imagine with an Empulse R I would see around 20-25% longer range.
I don't really view it as $/mile though - the S has "enough" range for my around-town needs, it's more a question of whether the Empulse has extra capabilities that I would use. The fast charger makes limited touring *possible* if not ideal, assuming you can find a level 2 charger; very few installed in my area now, but that may change in the next couple of years. The extra range at high speeds would make trips down to visit mom (80 miles away on 50-65 mph roads) possible, even if a short layover was required halfway between. The extra performance? I wouldn't turn it down, but I don't do track days and I can already ride the Zero faster than I should on public streets. It's bragging rights and sex appeal, which are fine by me.
Keep in mind by the time Brammo is building the Empulses (and clears out their preorder list), Zero may be getting ready to reveal their 2013 bikes. Noone knows what those will look like - surely they will continue to use the EIG cells, but Brammo has a supposed battery advantage now.