|The Mighty Grognard
To the OP,
You should not penalize the player for using his/her powers wisely because Wisdom is the hallmark trait of a druid. Rather than viewing this as an exploit, I see this as a player succeeding to rise to the challenge in terms of roleplaying his character both in character and out of character, to overcome the obstacles that are set before the party for their mutual benefit.
Let me break it to you this way - Smart players are going to do things that you don't expect. That's the great thing about playing a game with people who use their heads as opposed to those who don't. A good DM rolls with it. To deny your players access to their character's powers based on your personal frustration would be unfair on your part and could do more damage than good for your game (if not your friendship and good standing with your players as well).
That being said, I have found that the answers to nearly every rule conflict that I've encountered are written clearly in the books. In this case, the answer is simple - earthglide does not let the user pass through WORKED stone (look it up if you don't believe me). Your interpretation may be a bit different than mine, but this means brick walls, tiled floors and other architecture in the game where my character has earthglide ability. This means that the player will retain the ability to glide in most natural places, but not in many man-made places. Apply common sense here.
As for the alternate elemental stuff - if it isn't expressly written, then you don't have to allow it. Period.