Upgrade finder is completely useless for less than max level toons, it would be useful if it only showed items I can get.
Spending time looking for upgrades instead of just playing and enjoying the leveling experience seems a bit counter-intuitive to me. Leveling doesn’t take long enough to worry about where the next upgrade is coming from.
You can, almost exclusively, just equip your highest ilvl piece in each slot. If you’re using heirlooms it changes though as they’ll be better until max level, either the level cap or the maximum level you upgraded the heirloom too.
I don’t know anyone who enchants items while leveling either, perhaps if you’re an enchanter you might do your own gear just for the skill-ups though.
I just remembered that quest rewards can become rare or epic too, so you could spend time looking up an upgrade and then on your way to it get a quest reward which rolls as epic and is better than what you were aiming for.
The upgrade finder is only designed for max-level characters. We don’t have a lot of demand for low-level character optimization features right now. And as Cluey said, that is usually because people level up quite quickly and don’t hold on to any piece of gear that long.
Also, a lot of the calculations we use aren’t valid at lower levels – your abilities do different amounts of damage, stats convert at different rates, you may not have access to certain spells, etc.