Excellent points, both! If you have the room and patience for multiple antennas, then that is certainly a cheaper option that will perform just as well, if not better.
I don't know what kind of systems you are listening to, but if you are listening to a couple of different bands, you could benefit by using band specific antennae for each one. For instance, I plan to run four mobile scanners that listen exclusively to 800mhz systems off of one 800mhz antenna, and run the conventional scanners off of a VHU-UHF dual band gain antenna. The narrower the bandwidth of your antenna, generally the better performance you get.
Of course, a lot of people aren't in situations where they can separate their scanners by band, but if you can, it's a good way to go, performance wise. And if you're going to stick up multiple antennae, it just seems a waste to make them all the same, lol.