Supposedly, the aftermarket wires have less resistance than the factory wires, as far as longevity goes, I'm not sure. I've been using MSD wires for a few years now and have removed and re-installed them numerous times with no problems. As mentioned above, a little dialectric grease helps for when you need to remove them.

As for the factory wires coming apart, that's fairly common if you just try to pull them straight off. You have to try twisting them first to sort of break them loose. It can be kinda tough by hand, especially with the heat shields on, but it usually works. A pair of spark plug wire pullers (the kind with the red rubber coated ends) is a good cheap investment.