Should I modify my front bumper again?
 

This is my bumper now:
http://ecomodder.com/forum/attachmen...1&d=1417554586


Would I be better off filling in the area between the bumper and splitter like this?
http://ecomodder.com/forum/attachmen...1&d=1417554586

Where is the air intake for the radiator ?
Do you have a belly pan ?
The mod seems easy enough to do, even using a piece of cardboard.
So yah - go for it.
I would speculate that it might channel air over the hood a tiny bit more, but that overall, the difference will be negligible.

If angled up or rounded though, you might see more flow over the hood and it might lower the stagnation point.

BTW : I copied your wheel spats : http://i877.photobucket.com/albums/a...yb17/block.jpg

should I
 

Fiat research showed that a vertical face,or one which lays back slightly,has a drag advantage over one which is undercut.Your splitter is taking care of the undercut,but filling in the void makes for more sectional density.
If you watch the video of the T-100 at Darko,you can see how it will flow.

I'd say yes because those look like chains holding the diverter up, which won't prevent it lifting. So not so much for sleekness, but to stiffen the whole structure.

At Bonneville they used adjustable rods.

http://ecomodder.com/forum/member-fr...6-bedammed.jpg

Radiator inlet is currently where the plate is in the pic. I'd just have to move the shutters out or run a duct to them. Or copy your scoop! :D
http://ecomodder.com/forum/showthrea...ore-29966.html
http://ecomodder.com/forum/attachmen...1&d=1410549719
You can see the sagging in this pic which I corrected with the chains.

I have a partial belly pan, but I haven't installed it yet.

Are you kidding? This is ecomodder.com, and you have to ask if you should modify some more?