I think wishes were intended to be (and were in Gary's game) much more common than they ended up being in practice (every else but Gary's games). But almost always through magic items (rings, swords, etc.), almost never the actual wish spell (I never saw an 18th level m-u PC in all my years of playing -- I'm not even sure we had any 18th level m-u NPCs). There are numerous magical effects that only a wish can counteract (as well as some that even a wish can't counteract), guidelines for appropriate uses for wishes (raise characters from the dead, heal the entire party, transport the party to safety, etc.), and the limitation in the DMG that it takes 10 wishes per point to raise ability scores above 16, etc. All of which suggests to me that wishes were intended to be both relatively common and certainly not limited only to high-level characters/campaigns (if anything wishes are more useful at lower level, where characters have fewer options).
I think wishes were less common outside of Lake Geneva because DMs were afraid that players would use them to wreck the campaign (either by making their characters too powerful or neutralizing the bad-guys) which led to the practice of DMs twisting the wording to punish greedy players which led to players being afraid to use them even when they had them (even for non-greedy purposes) which led to a whole mystique growing up around wishes as something you heard about but almost never saw in actual play.
In our group back in the 80s wishes were rare but not unheard of -- maybe 3 or 4 total used over 5 or so years of play. In the convention game I played in with EGG in 1988 (Necropolis) we used at least one, possibly two, wishes to save our party from otherwise-certain death.
