On self-contained vs. central battery and wires, I like the latter for flexibility. I haven't gotten the switches yet, but when I do, I'll be able to control everything while riding. Also, I can and like playing around with my lights, so it makes it easier (and cheaper, I think) to keep playing with the system. 12V automotive parts or other 12V gadgets and gizmos are easy to come by, so I think it is a very convenient sort of system. Of course, if you haven't the foggiest notion how to wire things up and a soldering iron terrifies you, you might think a little differently. On the other hand, it isn't that hard to learn enough to start putting a system together.
Tor
Flexibility? Care to elaborate on that a bit more? I would think flexibility would decrease because you have to route wires, and figure out where to put a battery pack; with a self contained system you have none of that extraneous stuff to worry about, plus there's less to go wrong with pulled wires, bad connections etc. It is true, I don't like doing electrical stuff so making it simple with a self contained system is more to my liking, but regardless, simplicity equals more flexibility, not the other way around...at least that's my opinion.