WiFi Extender Antenna - do they work?

I have seen mixed results with extender antenna's, I bought a second router on black friday for 10 bucks from Tiger direct and setup it up with DD-WRT as a repeater bridge. This would probably serve you better, it is a fairly simple process.

I am not sure why you replaced your router's antennas. I got a refurbished Cisco refurbished range extender for 39.99 and placed it around the center of the house. Now with the wireless router at one end the other end of the house has coverage as well. It seems I periodically have to unplug/plug it to reconnect bit not now I have coverage for using iPads in the bedroom. Pretty much plug and play for setup.

Range extenders can help, but it depends on where your router is and where you are trying to get coverage. Stock antennas will tend to be more omni directional. High gain antennas work by focusing/directing the energy in a new pattern. (so you are sacrificing coverage in some directions to make it better in others) Ideally, you'd need to see the antenna patterns to know if it will help you.