I was with you up until the part about "great grunge was never dumb music like 80's metal". To be fair, 80's hair metal could barely be called music as it was 85% image and 15% music. Even the "best" bands of that genre didn't do their best work until they shed the glam image.
However, REAL 80's metal - IE, the underground stuff - produced some incredibly intelligent music (maybe not as intelligent lyrics, but truly intelligent music). Even though they've become cliche' now, Metallica's 80's output is still incredible if taken in context. They were experimenting with compositional ideas that hadn't been used in popular music for a long, long time. They almost had a progressive style but still embodied metal.
On the heavier front, the underground death metal movement begain experimenting with even more radical musical ideas. And even Iron Maiden - whose image may be really silly - are still a musical force to be reckoned with. I don't know of another band that has written more memorable melodies and hooks throughout the years as they have.
So don't be so quick to put down 80s metal. Throughout the years, metal has been one of the few genres to continually progress and evolve and take on more and more complex musical ideas. It's not the dumb, testosterone fueled genre it was 30 years ago. As intense as it may get, the best of it is also really intelligent too.