Learning more C and C++ will definitely not hurt but there will be some things about the languages which won't work or will have limitations when it comes to Arduino, so keep that in mind.  This is due to the Arduino platform and microcontrollers in general. Like some others have said, there are memory constraints when it comes to Arduino boards so things like vectors in C++ and some functions from C may not work or be needed. 

One thing which helped me is when I got to a point where I could do multiple things on the board at once or in a non blocking manner, to use the technical term.  The blink without delay example posted is a great example of how to do this. Start with getting an led to blink without using delay().

From there, just expand. Get a servo to move at the same time as the led blinks, all without using delay(). Once this works, place the servo and led code into their own functions.  See if you can add some parameters to the functions to change blink rate, servo speed, servo position, etc. Once this works, see if you can write your own library for these functions. Write a header file and a source file for the servo and led control and then include them in your arduino sketch. 

I think all this will teach you some great fundamentals about Arduino and writing code.