Personally I think feys are too fragile to fly at high altitudes - though across a stream shouldn't be a problem - but that's likely more game mechanics.
even take to the air is limited though to a short hop...the z axis looks cool going up and down but its really only about 50 feet in movement
Would you be willing to sacrifice lock-picking for Take to the Air?
The problem with what you're suggesting is that it sets a precedent. Everyone with a flying familiar is going to want their familiar to be able to take to the air as well. There just isn't the time available to devote to redoing every familiar and every potentially-flying polymorph or shapechange.
Not sure how much of an impact that would have on the "special-ness" of the ability.