Gear improvement: where to invest blood shards?

Wizard playing Vyr/Archon here.

I have reached a point where all my pieces are ancient, with no obvious turd. Many can be improved, but it’s difficult to assert which to focus on first.

How can I best decide where to spend my resources? This is especially acute for Blood Shards which can’t be collected in large numbers for later decision.

One criterion is cost, where pieces costing 25 should perhaps be focused on first (armor and source), compared to say, rings or wand.

Any specific reason to focus differently Legendary rerolls and/or Upgrade Rare?

Of course, I’d be happy to get specific advice if you want to have a look at my profile (https://www.d3planner.com/707207709)