Those shields need to seal to the hood to work, so it has to be a tight fit. What are the top edges made out of? Something hard or soft? If soft, I wouldn't worry about it.
You should definitely get a before and after dyno to verify it was worth it.
I'd consider replacing those filters with K&N's that have exposed filter area at top.
Some evidence they outperform the G3's...
http://www.myg37.com/forums/intake-a...xflow-cai.html