I'm kind of thinking now...and this really has no baring on the discussion of organization of the planes [so those that will can skip it]...but it just occurred to me, I would like/think it might be cool if, for the Faerie and Shadow planes at least (whether they keep to this "getting closer to the Energy planes" story element or not), going there actually changes your character to "fit/match" the plane.
That is, human characters become elvin/sidhe versions of themselves. Dwarves, maybe, stay the same or take on a slightly trollish or goblinoid look. Halflings turn into Brownies. Elves and half-elves, no doubt, look the same or perhaps a bit more regally "elfy" than usual.
As the blaring yellow light from the dimensional portal evaporates before your eyes, you find yourselves standing amidst a group of faye beings. From the muscular bulk, the reddish hair and braids, and traditional family battle axe in his hands, you can tell the broad shouldered elf before you is your barbarian warrior friend, Grod. But he has pointy elf ears, almond shaped elf eyes and finer facial features, his normally scarred leather armor and pelts have been refined with elegance and clean white ermine pelts! You turn to a brownie standing at your knees tugging on his new russet and brown leathers. The swarthy complexion looks up at you and from behind the now long pointed nose stare the unmistaken brown does eyes of youru halfling companion, Gilbo. "What's happened to us?!" Your druidess, Galinda, as you can tell from her face and the spear she carries, looks around and down at the gown and cloak of leaves that now surround her dryad-like golden skin and spring green hair, says, "I think we've made it to the Land of Faerie."
Let them keep their armor and weapons, skills/knowledge and the like don't change, magic doesn't have to change or perhaps takes on a slightly more faye/shadowy form or slant when cast. Maybe give them a temporary enhancement to their Cha. and/or Dex. Maybe some minor natural ability to match their new form.
Same on the shadow plane, turning darker, wispy, goblinish, shadow-spectre-ish...all of your adornments, skin, hair taking on shades of grey and black...
...and maybe the longer you stay on the plane, the more like your transformed form you become. Beginning to take on more of a faye or shade attitude, until you forget you were ever from the Material in the first place. Hopefully the PCs notice and realize they can't stay there indefinitely...or do they now feel they want to?
Makes for a cooler visual, I think and gives a bit of added "other worldliness" to planar travel. ...questionable whether I would do this on the elemental planes, but being infused with the [positive/negative] energies seems totally plausible to me.