Works headset has made a big difference to both bikes i’ve used them in- lowers BB a little, slacks head angle a decent amount, and doesn’t mess with the suspension at all.
For the bushings, you do need the clearance- since it shortens the effective length of the shock, the bottomed-out position is also shorter which can mean clashing hard parts on a tightly packaged frame. I got some 3mm ones for my Hemlock but that was too much and left the chainstays whacking the seat tube. Also, it may slightly change the suspension rates, though whether you notice or care is a very different question 😉