Help w/ improving dash speaker fidelity...

I've got an older car. The front speakers (4X6s) are mounted in the dash corners face UP from 'inside' the dash and
basically focus right on the windshield. I'm going to be replacing the ancient original 4x6 speakers with new ones. What
I'm wanting input on is this:

The bottoms of the speakers are opened to the cavernous dash (remember it's an older car) and ultimately the footwells
below. One speaker sits above the speedometer/tachometer area, the other above the glovebox area.

1) Should I install them as is, 'open' to below?

---

2) Should I consider enclosing them somehow from behind perhaps for better sound? -
Some possibilities...
XTC Baffles mounted behind the speakers facing up (have to be glued in)
XTC Baffles filled w/ some sort of insulation materia
Simply some insulation batting attached to/around the back of the speaker and under dash
...

2.1) And if so should I go w/ the standard 3.5" deep baffles or the slimmer 2" baffles?

2.2) Water shouldn't be an issue but just in case - should I 'port' or cut any holes in the bottoms of the baffles
either for water or sound?