The difference between things of instrumental value and intrinsically value is the difference between means and ends. No matter how you twist the happiness story, it always is that it is the "end" we want to achieve. That distinguishes it from things of instrumental value which cannot be the target, so to speak.
Thus, happiness is distinguished from other things in that it is an end to our endeavors. Therefore, happiness is of intrinsic value.
If you go by your understanding, everything will be both instrumental and intrinsically value. This is something which is interesting but useless.
