Ijust got a 2.6m discus CS ARF with the air brake and retract. The thing is, Idont want to use the air break or the retract. My plan is to simply leave the covering intact over the brake slot and screw a plate over the retract bay. OR maybe even fix the door in the closed position, but then the stock door is a bit flimsy so maybe not.

ALSO I'm thinking this will save some weight, with the absence of the extra servos and stuff.

So my question is; will the plane fly better with less weight or does it even matter?

You can just tape the gear doors. I tape the gear doors on my ASW28 and 17 when I'm at the slope.
Leave the airbrake as is. I have an Pilatus B4 that will glide forever if I don't use them. The same with the ASW's.

Have you tried Flaperons instead of the airbrakes?