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KAuss sounds like our commute is similar lengths (I do 80 mile per day, and have done 146,000 miles in the 86).
Frankly, if this is going to be your commuter car, you are putting too much emphasis on the torque dip. If you are doing commute driving you don't notice it, and if you are stepping into the throttle you're going to be above it anyway. Honestly if someone had shown me the charts, I wouldn't have known it existed.
If you need room, the MX-5 is not the solution (check out my "Junk in the Trunk" thread for how roomy the 86 is).
For overall value I don't think the cars are close in comparison, 86 wins hands down, particularly as a commuter car. But, admittedly, I'm not a fan of the Miata, and while the newest is a better looking car than the previous ones, I still think they look like bathtubs on wheels.
As far as the "rent space when you need it" mantra, I'm not a believer. If I'm throwing down nearly $30K or more for my DD it needs to fit 95% of my daily driving tasks. Renting a car is just to inconvenient to have to do it on a regular (or even semiregular) basis.