One thing to note in flightless Faeries, is their productive and often useful nature. A brownie would not be quiet so dutiful to their cleaning and choirs if they could flitter about. Nor would Dwarves be able to travel through mines with the easy that they do, if they had to cumber about with gossamer wings large enough to support their brickish frames. Which brings up size. Often winged Faeries stand no more then 120mm, while flightless Faerie can reach a size equal to an adult Man, and in some cases, though rare larger.
This evaluational divergence can be compared to the avian and mammal separations from early Dinosaurs. In both hunting practices and brain mass, in ground and flight Faeries, have caused them to evolved in drastically different means. This is not to say flighted Faeries are not capable of being clever, only that they tend to not share the higher intelligence of Ground Faeries.
In close, remember to enjoy your preservation of both air and earth, remembering to leave no place unexplored.