Question - Do valves generally tighten or loosen with wear?
Should I do them at the tight end or the loose end of the tolerance or in between, like I originally did?

...the bikes I've owned and serviced I have found the gaps increase with screw and lock nut and tighten up with shims.
Probably best to set them in the middle of their tollerance like you have then once you've checked them a few times at each service you can second guess whether they'll tighten or loosen, THEN adjust to either end of the tollerance settings to give you more miles before they need checking again.