As my neighborhood starts to buildout, I'm noticing more wireless access points popping up from new neighbors and crowding the spectrum. This occasionally caused problems with dropouts, especially noticeable with I'm using Airplay to remote speakers around the house There are a few things you can do to fortify your network in a crowded area including trying to move your channel away from interference of neighbors and move to different frequencies. In attempting to tweak my Airport settings recently I learned that by holding down the option key while selecting the type of wireless network you wanted to create, you're presented with additional options.
There are some advantages and disadvantages to limiting the types of devices on your network. In my case, all my devices are capable of 802.11n speeds so aside from the occasional guest who may have a lower speed device, I didn't see much disadvantage of creating an 802.11n only network. You can play around with the various options and see what works best for you. Since moving to an 802.11n only network at my house I've found the reliability of my Airplay wireless streaming has been significantly improved.