Where can I see Hokusai's Great Wave today?

What's the advantage of seeing an original piece of art over a serviceable replica? Especially in the case where the "original" is a print, one of dozens.

Obviously "serviceable" is doing a lot of heavy lifting here, a replica might simply not be very good, might not capture some vital characteristic of the thing which makes it a great work.

But otherwise, it's basically that the knowledge of how important and significant this work is puts the viewer in a more receptive frame of mind, right?

To be clear, that's not nothing. I of course know firsthand how much that affects the impact of a painting, museums and galleries care a lot about how they display their collection. But is that it?

As you say, some works seem to lose something in any reproduction. La Giaconda (Mona Lisa) is a great example: any reproduction you may have seen in books or online hasn't captured the rainbow of background color in the original, or the sensation of viewing a living person sitting for a portrait when viewed at a few paces in the Louvre.

The original one is behind an extremely thick layer of glass that completely distorts the colours.

It is now, but it used not to be...

The Mona Lisa has been behind a thick bulletproof layer of glass since 1956.

I'm kind of surprised actually that they haven't found a better way to exhibit it in close to 70 years. But the protective layer is a big part of why it's underwhelming in person.