I haven't noticed any difference in idle quality or performance, so far. I am doing my first mileage check right now. Like the 06's, I am losing the redundancy of the stock system, and if I lose a coil, I'll lose the whole cylinder. The stock setup would still fire on 8, but that affected cylinder would only have one plug firing, since the coils fire twice per cycle. I do want to go back to the races in a few weeks, with a fellow forum member who has the stock setup, and have him do a baseline run and then unplug his stock wires and put my shorties in and make a run. If done within an hour or so, it should give us an idea whether it does any good, or not.
If I hear of a mod. and it appears to me to have merit, I give it a try and see for myself. I'll give it a fair shake, and if it doesn't appear to do any good, I'll put the stock system back on. As examples, the MDS "on" light I did works great and helps mileage, as arnoldw can attest. My double wall triple insulated intake duct does little except keep intake air cooler in town, and recovers quicker. On the highway it doesn't appear to do much. Adding another 3 in. duct into the front of the airbox definitely helped, both in town and on the highway. See Phase 3 of my mileage tests and referenced threads at: http://www.300cforums.com/forums/showthread.php?t=9732
Vortex generators (heaven forbid) help keep the Magnum rear window cleaner, but only on the highway....in town, nothing. I am going to add some under the vehicle (in front and in back) and see if that helps any. My rich/lean controller shaved two tenths of a second off my 1/4 mile time, but I still need to do a little more testing with it. Acetone (another heaven forbid) works to some extent....mostly on the highway. My best mileages 30.3 and 29.8 mpg were both achieved using about 6 oz. of acetone in the tank. The most important factor to me is the fact that I love to tinker and experiment, with a goal of better mileage and performance.