Welcome Coal.....
Doing "mods" is all in the idea of who you ask and what you want. At 72, your at the Coast Guard sanctioned speed limit now.
I've heard the grates allow your pumps to get water quicker and less cavitation because of a fin that directs water directly into the middle of the pump.....
The impeller change....if you change your pitch one way or the other, you'll normally be giving up the hole shot for the top end and vice versa. Solas makes some nice impellers, but for me, the mods aren't worth the cost. The performance change is there, but not going to make it leap like you may think it will.
I spent $1300 bucks on my computer cause I thought it was slow, so I built my own with all the top of the line products and an SLI ready motherboard. Well guess what? I still have to wait on pages to load. Yeah, there a bit quicker, but I wanted them to be there when I went "click".....
My point.....if you blow $500 bucks on an upgrade, don't expect it to get some kind of unrealistic advantage. It won't happen.
Now, if you want to mod out the engine for racing.........that's where you'll see big power.....but those engines only last a season or so before a rebuild is necessary.........