i'm not sure what the regs are in the USA but in Canada the 15 and 20 amp outlets are different and you can not plug a 20 amp plug into a 15 amp receptacle as the prongs are different. 15 amp both prongs are vertical with the round ground prong bottom center. 20 amp have one prong vertical and the other horizontal and the ground bottom center. you can also get locking receptacles and plugs that rotate to lock in place they are different again but maybe an interesting upgrade as they don't come loose unless you rotate them.
to be honest just pulling your plugs and re-plugging them from time to time makes a difference. It cleans the contact area. I'm sure a lot of what people think they hear as a difference is in actual fact just a reseat of the plug making better contact when they pull them out to re install new upgraded plugs sockets etc.
