I've always been fascinated by the classical elements, and for whatever reason, I thought the quasi- and para- planes were quite cool, along with the Negative and Positive.
I know there's a lot of varied cities and strongholds in various planes, especially the four main elements, but these seem like they'll just make for city or castle adventures with an interesting window/sky view.
I'm sure that a skilled GM could make a fun and interesting "wilderness" adventure in the Inner Planes, but I'm not really sure how.
There was an interesting idea in one of the recent articles about D&D 5th where they touched upon cosmology.
Essentially there were different parts of the elemental planes, sort of radiating out from the prime.
Close to the material plane it was not that different. If we start moving into the Elemental Plane of Fire we could start out in a very hot desert, going through a plain of ash and volcanoes where there is more and more lava and fire, until we reach the fiery heart of it.
Just a thought that may make the elemental wilderness easier to play in.
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Henrix