I get regular seat time in my mother's '06 987. Here's my take:
1. Acceleration: It feels quite similar to my '04 986, just a smidge peppier due to the increased output. I drove it last a few nights ago and inadvertently made racket off the stop. Oops.
2. MPG: Seem to be about the same, 24-25mpg.
3. Stereo: Oddly, mine sounds better in terms of bass depth. Neither one of our cars has the rear speaker package installed, and with the radios at the same audio settings mine just sounds better.
4. A/C: Hers doesn't have auto climate (I rarely use that feature in mine), equal in terms of output. Hers has heated seats, though.
5. Handling: Equal.
6. Exterior: I prefer the 987's lines over the 986. There, I said it.
The panel gaps are much tighter, the revised door handles, and the aluminum frunk/trunk lids are nice touches. Still love me some 986.
7. Interior: Disappointed the center console cannot be removed a la 996 GT3. Room seems improved with better packaging, especially in the driver's footwell. Material quality is a bit higher though some surfaces seem more prone to premature wear than in 986s. Door pockets are narrower and more difficult to use in the 987. The centrally-located spoiler switch is a nice touch, as is the Homelink.