Should I see a difference with the upgraded SCOPE?

I always bring 2 snipers in my squad, that are equipped with a SCOPE.

I upgraded the SCOPE in the foundry, and the description of the upgrade said something along the lines of "highlights sensitive areas in the target"

However, I didn't notice anything different in the following field mission, is the effect noticeable or is it just increased accuracy with no visual difference?

I don't need to build new SCOPEs, right?

The "highlights sensitive points" is just flavor text. The effect of the SCOPE upgrade is a 10% increase in the likelihood of critical hits. There is no change to weapon accuracy.

This boost applies to ones you already own, as well as new ones you build.

The XCOM Wikia says that this is bugged, but it appears to just be a bug in the display logic. According to their article, you won't see the 10% bonus unless you pull up the "additional info" screen.