SilverBurgie,
It would be interesting if you would run a mileage test before you install the XXL screen, and then again after. It would be interesting to see if you get similar results. Riding behind the Clearview XXL is very comfortable, but the trade off in lost performance and fuel economy was huge. I may have to go back to using it at some time, but for now I am trying to learn to live with the stock unit. The old design Clearview XL that I had was not as bad - I got 47 -48 mpg with it - and it was still pretty comfortable. I wish now that I hadn't sold it.
A quiet helmet is definitely key to riding with the stock screen. My older Shoei RF-800 is the quietest of the three helmets I own for that. The RF-1000 is a completely different design. Sad to say, it doesn't fit my head right. And Rider Magazine agrees with you that the RF-1000 is not as quiet as the previous models. I always liked Shoei's, but they have eliminated me as a customer now due to the new design.
Bugs. You'll still get them of course. You'll just be wiping them off of the Clearview instead of your faceshield.

In truth, it is easier to wipe a faceshield that that big windscreen, but bugs won't hit your hands anymore, and you won't go cross-eyed when a big bugs splats right between your eyes on the helmet faceshield...
I don't carry anything in the trunk usually except for my regular glasses, sunglasses case, a hat that I wear when I get off the scooter and maybe my bug cleaning stuff - no real weight or bulk to any of that. I use it when I stop to stow my helmet, jacket, gloves, etc. - same plan that you have. The stuff that I want to have with me, but access less frequently, goes under the seat. I did miss the trunk when I was riding without it.
Enjoy your new accessories when you get them, and be sure to give us feedback on your satisfaction with them.