I don't know if the end caps have anything to do with the sound, but I'm liking the way mine sound, even at idle...they'll bark, but at highway speeds you can still hear the stereo fine, and they've got a nice mellow sound. They slip on to the stock pipes, but to get the most out of this setup, you'll need the A/C and the download for the stock ECM.
Cooler? I don't have anything to compare it to, since mine were put on before delivery. The vented lowers work fine when you're moving, but sitting in traffic, this motor puts off some heat, and I don't think removing the lowers would help a lot. When it's 95 degrees here, and you're sitting on asphalt in traffic, it's probably 110, so engine heat is gonna' be felt. Even then, if I can roll at all, it gets OK.
Glad to hear that they're coming out with more pipes that aren't so damn loud, as I think the "man" is going to start paying more attention to that sort of thing in the not too distant future. The SE mufflers are just fine for me for the time being, and they might add just a little juice to the motor, but you could certainly get more by going other routes. But, I wouldn't put them on without the A/C kit, preferably 'Roll your own', and at least the download. I'm having no start problems, and no problems on deceleration. I was behind a Glide not long ago with Rhineharts and the thing was popping bad on decel...I don't think I could live with that.