The way I see the use of planewalking mages reminds me of reading languages.
I believe myself to be a proficient reader of English, able to read at a
very high level of comprehension. But if you were to place a grade school
primer in front of me that was written in Russian, German, Italian, etc. I
would be at a total loss. I know that the words are there and that they each
have meanings, but I would not be able to understand them. I would have no
idea what I was reading, but would see the words right infront of my eyes.

I believe that it would be the same for a mage. He would be able to feel the
magical power flowing through the land, but would have no idea how to
control it, shape it into magical spells familiar to him or her. Its power
would be out of his reach, his abilities diminished to the lowest
mainpulation of magic, (1st and 2nd level spells).

As I said in an earlier post, elves would not be able to cast higher level
spells at first, but due to their connections to the land, eventually they
would adapt, able to manipulate the flow of magic at full power. This is
like groups of related languages, such as the Romance languages. Although
knowledge of one does not instantly mean you can read a related language,
with time and practice, it is easier to pick up then it might be for others.
For humans, their BL acts almost like a translator, working to convert the
flow into a usuable form. Otherwise, they cannot understand the flow, except
for rudimentary magic. Therefore, without a BL, a 20th level planewalking
human mage would be almost helpless. ::evil grin:: Come here, Elminster....

All this is IMHO, of course. Any other comments?