In my games, the Planes are exotic places to visit, some plot devices to bring in creatures and concepts that could not exist within the campaign world, and so on and so forth.
When the plane traveler looks at the ethereal sea, what s/he sees is actually what he wants to see. Which then is communicated to other people when this traveller returns, people who travel, some of them seeing the same thing, some others not, which means that even though the image of the ethereal sea and mist and ships is something of a common tale, this isn't the only one told by plane travelers.
I also think that the planes aren't just "space", but "space+time+potentialities". What do I mean by that? There's isn't just "one" material plane. There is an infinity of different material planes. My meta-cosmology assumes there are several multiverses and all possible worlds do exist. In fact, to take a particular world as an example, there isn't just a single Praemal but an infinity of them with different alternative histories. Then there is an infinity of Greyhawk, and an infinity of Forgotten Realms etc.