Fiber really isn't all that more expensive than many other options. The cabling, especially for install purposes is relatively cheap (definitely not as cheap as cat 5).

The connectors can be an issue over time, depending on which kind you get.

In all actuality, a Manual patch bay will probably serve you better with regards to delay than a matrix. Essentially, any time you have some form of a "smart" device inline, its going to add some delay, anywhere from one field (half a frame) to 2-3 frames, it all depends on the quality of the device. Most of the time, I find that this added delay is really not an issue at all, as the sounds, etc is all going through similar delays usually and in the end, it normally works out for 99% of the things we do. IF you are doing something like IMAG, or lip-synched stuff, you might have to get with audio to make sure they delay their signal just a bit to match.

Cat 5 is also very useful for control applications though, lots of the projectors today allow you to control things via IP. There are also lots of great devices to do serial over ip, so it works for older stuff too. Serial over IP is also a GREAT thing to have when working with Element Labs stuff and doing mapping, you can even do that over WiFi with the right gear.