I didnt see it in the double feature format and didnt care, since neither film felt like a 70s movie(and the use of cell phones and references to current affairs didnt help). The Restricted panther animation was the most retro thing about it. And the guy doing a Roddy MacDowell in Legend of Hell House impression from the Dont trailer.
And Death Proof's opening credits.

Planet Terror seemed very 80s--however, i really enjoyed it.

Hated Death Proof.

I saw PT separately first a couple months ago--and they had squeezed the image like you used to see with movies on tv. The last one I can recall that did that was Die Hard.

I loved both entires from RR and QT

I agree, PT felt more early 80's horror film than grindhouse and Deathproof felt more straightforward 70's than grindy. But, I was not unimpressed. Total fun.