Have other designs for individual gasper ventilation been tried?
Whether or not they have been "tried" is probably not answerable, as "try this" type designs typically don't make it into production aircraft. 

Look at the simplicity of the existing system, its simply some lightweight ducting with an adjustable air vent above each seat. The entire system has no other electric or adjustable parts, so maintenance is pretty easy, as well as reliability. Its also probably a hell of a lot easier to get certified. 

Putting little fans above each seat wouldn't have any benefit here, as the air they move from one side of the fan to the other side has to be of a significant volume anyway, so you would still need ducting. The fan speed would be controllable, but then again so is the orifice size of the existing vents, so really no benefit there other than complexity and more wiring/electronics. 

The existing system also works relatively well for individual climate control. Unlike in your car, you don't have a large space between you and the person next to you, so getting "individual" control is difficult (Seat A at X degrees, Seat B at Y degrees, etc). But note that even in your car you really aren't adjusting the heat or cold temperature, but the fan speed either through the AC system or through the heater. The heater and AC are at a constant temperature all the time.