My guess is no. Most wireless networks out there already have more than enough bandwidth to meet any internet requests you can make. The bottle neck occurs when you hit you internet connection. You are only getting that 300 kb/sec from your cable or dsl connection. Your existing wired or wireless network should already have more than adequate bandwidth for your current internet connection.
The only place you will see improved speeds for this is when you are doing stuff across your own network. Transferring files or something like that --> applications where you aren't using the internet, but simply your home network.
nope don't get it airport is 11mps +/- and airport extreme is 52mbps +/- then your router or airport hub connects to the internet at 1.5 mps tops unless you have t3 or somthing even t3 i believe wouldn't be hindered by standard airport. if you get t3 plus then you might want to get extreme. the other reason is extreme has better range which might be nice.