I just made a little test for you.
The choices presented to you in the "Load a view" dialogue depend upon the media types listed, and also the "view info type" (is it a playlist or a library view)
For example, as you have observed, a view saved from a playlist or smartlist won't be offered for loading in a library view, and vice-versa. Also, if you have audio files listed in your view, you will only be presented with choices that include audio files (or something like that). It all gets very complicated, very quickly
So, in my little test, I saved library views that listed only audio, video, image and data, then finally, saved one that listed all four.
Each view name began with the word "Library".
I then made copies of each of the five .jvi files, changing the "Library" in the filename, to "List".
Next, I opened the .jvi files with UltraEdit. UltraEdit is an advanced text editor, Notepad++ is a freeware example. When I tried using Windows Notepad, it was presenting the text as one huge block, even with wrap turned on, whereas UltraEdit displays each entry on a single line.
All the way down at the end of the file, there is an entry like so: <Item Name="View Info Type">2</Item>
"2" represents a library view
"3" represents a playlist view
When I changed the two's in my copied "List" files to three's they showed up as 'load a view' choices for playlists and smartlists of matching media types.
At the top of each file, there is a line that goes like so: <Item Name="Media Types">1</Item>
"1" = Audio only
"2" = Image only
"4" = Video Only
"8" = Data Only
"15" = All four of the above
Perhaps that's enough to get you rolling?
If it all goes horribly pear-shaped, don't blame me, OK?
I tested loading a hacked view both ways and nothing appeared to break. Predictably, when loading a view that was originally a playlist view into a library view, there are no categories applied, but that's to be expected as there are no panes in playlist views.
Good luck
-marko.