I think the newer style stamped-metal baskets hold a bit more coal than the old wire-style. I have both of them, and use them for different things, but I do find I use the newer style baskets more (tip: if you are ordering directly from Weber, you can get the individual baskets for much less than buying the pair of them).
One place where the old wire style baskets excel is in their height-- they bring the coals right up under the top grate on a 22.5. So they are great for searing stuff. When I cook pieces of chicken, I like to push the wire-style baskets right together in the center of the grill. I sear off the pieces briefly, then move them to the outer circumference of the kettle where I get some great indirect heat from the sides (and top) of the baskets. Works pretty well.
I have the plain rails as well, and use them even less often. They are just not as convenient, especially when I often light my baskets right over the burner on my SS Performer (a beautiful black one, in case Marty wants to trade ;-). But the thing I use the rails for a lot is a tip I found from one of the geniuses on these boards: the rails make a great spacer to allow you to elevate an extra bottom grate up much closer to the food grate. This is perfect for searing steaks, cooking corn on the cob quick, and (especially) for quickly cooking thin pieces of fish. So I think the rails are a good investment as well (though you could use fire bricks or something similar to elevate your grate).