I'm also not impressed with the front drive bays on the 750D - It spoils the design as soon as you fit something into them.
Corsair should look at some sort of 5.25" plates that they could easily provide so that any additions can sit flush with the rest of the front rather than sitting recessed in and exposing the cheap looking plastic behind them
If you look around there are tutorials for creating stealth covers - I agree this should not be down to the end user to resolve though.
I have the 450D and the airflow is superb with the front mesh panel, the only downside is that the front mesh is very coarse and therefore not very effective at filtering dust.