I have a theory...
The theory is, people in Biblical times were all from Missouri, they had to see it to believe it. So God had to pull a few tricks to get these people's attention, that's why there were a lot of Visions back then. Anywho, just a possible explanation.
As far as whether it's real or not, I know it exists one way or another, it could be a chalice, or it could be a blood line, more practical theory, you never know. But some of you guys have it wrong, the Grail doesn't have healing powers, Spielberg took the Bible's talk of 'Blood of Jesus Christ giving you eternal life', he simply took the spiritual facts and made them into a cool visual feast. So you see, it didn't have powers, Jesus could have used it at the last supper, but you never know. Over time it has been mixed with myth to where nobody knows for sure.
Now, if it weren't an actual object it would be the blood line, shoot, I forgot all these names, been so long since I really studied it, but there was a Rabbi who wrote a book, he talked a lot about stuff like this, made sense, I'll have to search around for the title, but he laid it out. And he was a Jew who believed Jesus was the Messiah, so he was coming from a true believer's perspective. Anyway, it's one of those mysteries, but if we did ever find out the grail was a real object and it existed and we could prove what it was, it wouldn't do a thing, just make for a very cool cup.
As far as God giving powers to an inanimate object, look at the Ark, it's what the Bible says he did, he 'lived' in the Ark, now I know, God is everywhere, this is one of those things that gets tricky, it's God's way of playing with our heads I guess, but that's what he says. We got a guy in Ethiopia who claims to have the Ark, he says that he can only approach it. Why is this bogus? Cause when Jesus died, the covenant was complete, and the veil was rent, and the Ark was then just a gilded box. If you still don't have a clue about what I'm talking about, try reading Luke 24, that talks about the death of Jesus.
But anyway, just my thoughts.