When farming TU's in normal sure it's already pretty quick and convenient, but personally I feel just a little hint of frustration when I upgrade something for instance from t2 to t3 with the 2 x Arcane Crystals and immediately on the next run, it drops the t3 variant.
The idea I had in order to rectify this would be to add a recipe that costs:
Unique you wish to upgrade (let's say Lavadome)
1-3 arcane shards depending on tier
A duplicate of the unique you wish to upgrade
Maybe the duplicate Lavadome in this instance, depending on its tier relative to the target unique you wish to upgrade, could influence the arcane shard cost for the recipe.
This is of course assuming that the recipe recognizes the higher tier unique as the target.
It's probably dumb and lazy, but personally if I were to use a feature like this, it could make looking out for those same TU's dropping just as exciting, easy to remember and it would feel rather rewarding - gets us through the tutorial easier.
Thank you for taking your time to read this, if you do.