I would like to know if there any difference between the new Wii Remote Plus and the couple Wii Remote + Wii MotionPlus
I wonder for instance if the "plus" gyroscopes differs in quality.
The sensor capabilities of Wii Remote + MotionPlus and Wii Remote Plus are the same.
I am not an expert but I personally tested both controls and I didn't recognize any differences in response and sensitiveness.
A Wii remote has the basic functions of the accelerometer and sensor bar sensitivity, but it's noticeably different: the on-screen cursor jerks around, you have a 50/50 chance that you might hit the basket in a basketball game, and sometimes it takes a while for the Wii to update what's really going on with the remote (my cursor has registered as being upside-down, while my remote was right side up!). The MotionPlus accessory is supposed to enhance the Wii remote's accelerometer and sensor bar sensitivity, in order for the Wii to register your responses in real-time.
A Wii RemotePlus has the very same capabilities, except they're built-in.
So, in answer to your question, there really is no different between the two remotes when used as you described, but it's better to have the RemotePlus simply because it has MotionPlus built-in, and is not near as long nor as cumbersome.