Just on the idea that lots of bands aren't 100% forward thinking, etc.
I can't speak to Porcupine Tree's first few albums. Never heard them.
But when an artist is inspired by certain things and incorporates those sounds (be they 70's, 80's, whatever) into his/her music, that is one thing. When a band just sounds EXACTLY like bands from a certain decade or style that is long established, and have began their career in that sound, it's a different thing.
You can grow by incorporating older elements into your sound. But then you just create your sound out of older sounds only, it's not forward thinking at all.
Not saying it's a bad thing, or that no one else does it. Plenty do. But it's very different than paying homage or something when you're already established.