A bigger diaphragm will not buy you anything if you want to increase range. The problem with extending range is that the further away the desired sound source is from the capsule, the more the signal-to-noise ratio decreases. Everything will get amplified, so that won't help, either, unless you pass the signal through a band-pass filter. If all you are interested in is the human voice, using a pass-band between 200 and 3000 Hz will capture most of the energy in the human vocal tract with telephone-like fidelity- certainly not hi-fi, but possibly good enough for your needs. Unfortunately, there may yet be plenty of ambient noise in that same pass-band, but I digress...
What sound professionals call a "microphone" is much more than just a naked capsule. The capsule is just the transducer- a device for converting acoustic energy into an electrical signal. A transducer does not become a microphone until it is housed in a carefully-controlled acoustic environment, designed with a particular sensitivity pattern in mind.
Most cheap electret capsules are omnidirectional, unless they are vented on the opposite side- in which case they become directional. While that would help, you still need an acoustic "lens" or interference tube to improve the sensitivity of the naked microphone capsule.
You can try a parabolic reflector, or build your own "shotgun" mic. There is much information that can be found on the intertubes. Perhaps you can start with this:http://en.wikipedia.org/wiki/Microphone ... irectivity
Do a little reading up first, to understand the fundamentals.
It would also be helpful for you to give us an idea of how much range you are looking for, and if the output of the changer will be amplified and played through a nearby speaker, or used for some other purpose. If the former, you will have the additional burden of having to control acoustic feedback- which will, unfortunately, be aggravated by the increased distance between the microphone and the desired sound source.