[glang]

The change of springs is usually done if the rider weighs more than the original springs were specced for. Then you have to verify the rate of the new springs needed for that rider. The best way to do this a sag test ie. check how much of the suspension travel is used up when the rider is on the bike and, if too much, higher rate springs are required.
Ive closed the small holes in my damper tubes and the difference is minimal. I have also gone to a thicker oil and prefer the feel but its always a trade off as the suspension has become harsher over big bumps. This is where the PD valves would help as they open with bigger impacts so reducing the damping and absorbing the force....