I must be in the minority. I've never focked with my Classic at all. Everything is stock powertrain wise. Motorboat mufflers, stock intake, stock tune, well, stock R3 tune and 40+mpg.
It's interesting. You follow the KLR forums and owners over there modify the KLR's, big bore kits, hot cams, PC's fiddle with the carburetion and loud exhaust (yeah, they have Kehin CVK's) and the mileage goes south, way south. The KLR is basically a lawnmower without a blade but mine is getting 56mpg. My stock Rock will stretch my arms anytime and attain speeds that will cause me to loose my license and my marriage but it gets 40+.
The parallel is....modify it for more (assumed) power and the mileage goes in the tank. At 4 bucks plus, I prefer mileage....and quiet.
I don't need to be Hardley like. Hardly riders put on loud pipes, the louder the better, and go slower even though they assume they are going faster.........I guess it's that mentality.
As for the stock exhaust pipes, I am not looking for performance, to me they are nice when you look to the bike from one side, but I would have rather prefer a one each side or a two each side combination better.
Maddogs are being made again. I have them and like them but kind of pricey for slip ons. If you want one outlet on each side check out Jardines. D&D are two on one side. Personally I like the two and one set up, only bike made with that set up.