If they had given this the Grindhouse treatment, with scratched-looking film, jump-cuts, and a damaged-sounding soundtrack, I think people would eat it up as an homage to the 70s-era Hammer movies.
I actually REALLY enjoyed this movie, but think it'd be even better given that treatment.
That wasn't seventies era. That was early eighties. Seventies was still very much like this. I take it you're not a Hammer fan?
Also what self-respecting fan of horror actually likes Grindhouse crap? If you deliberately make something look bad that's not a homage, that's poking an insult.
I really wish I could explain how and why I think the Grindhouse aesthetic is capable of being a valid artistic take on the horror genre, but...I'm not even sure how to explain it.
To extend an early olive branch, I think a lot of times the love for the style and nostalgia for films of the Grindhouse era is misguided. For instance, while The Texas Chainsaw Massacre may certainly qualify as a Grindhouse film (albeit a very well known one which isn't usually the case) it isn't an effective film because of its low budget or "Grindhouse style" at all. So if the style on its own is all you have, and no real substance, then you're not doing it right. So chalk it up to issues of style over substance in general.
But then sometimes you get films where the style is part of the substance. I don't think The Devil's Rejects would have been quite as good as it is if it were cleaned up stylistically. If the style is pulled off well and somehow manages to contribute to the film, rather than be its sole selling point, it can work.
Plus, there's another issue that I think is often overlooked: even if you're going for that sort of "fun", grimy, gritty, bizarre style, you have to take it seriously. To continue using The Devil's Rejects as an example, that film nails the Grindhouse vibe and yet it's not so over-the-top ridiculous that it's a parody of it. If I recall correctly Rob Zombie despises intentional camp in horror films and I can see what he means. Camp can have its place too, make no mistake, but it should be understood that Grindhouse style, camp, and horror are all separate things.
As far as this film having a Grindhouse style, I think it's already there. More so than other films because unlike a lot of the other pseudo-Grindhouse films out there, this one wasn't actually trying to be one. Argento wasn't going out of his way to do that. I think he wanted to make an old school vampire movie and a fun movie, yes, and perhaps he even intended some homage to the Hammer legacy, but ultimately the film ended up seeming a lot like the "Eurotrash" Hammer knock-offs that flooded Grindhouses back in the day. It doesn't need to look all scratched up and have a retro soundtrack. It's already a much purer Grindhouse film than the ones that do that intentionally.
So, to sum up my thoughts as best I can:
Is there potential artistic merit in the Grindhouse style? Yes.
Do many people misunderstand the style and use it poorly? Yes.
Does Grindhouse-style filmmaking have to be campy? No.
Are "Grindhouse" and "camp" the same thing? Hell no.
Would this film count as an example of that style? I think so, yes.
I only have one little point to argue:
That wasn't seventies era. That was early eighties.