The Workshop is too useful to ignore, but it's yet another drain on Blue Crystals. Therefore I suggest plowing the generous gem rewards from free More Events into Builders, Warehouse space (as needed) and then into purchasing Red Crystal packs from the Lost Realms Merchant to invest into leveling up Blue Crystal mines.
Once you do get a little ahead on Blue Crystal production blow these into Mass Craft at the Workshop. Then Sell All "Elite and lesser" and Collect All Legendary armor. Keep rotating through this until you're down to around 100k Blue Crystals.
Don't bother refining armor that isn't worn by a hero in order to save Workshop space.
Assign armor by these groups in this priority order:
* Healers and snipers: ATK boosts.
* Tanks: HP boosts, Crit Resist, Dodge
* Agile heroes (Stormcaller, Cheetalah, Doomrider, Suriel, Sun Maiden, Shady): Dodge
* Cannon and aggressive tanks: Crit, Acc, ATK
By keeping a lot of different types of Legendary heroes around you should have a sufficient Sanctum level so that you are only limited by Steel and mass craft and sell provides that. Note that while each level of refinement provides about the same attribute boost, each level after the first is more expensive. Therefore it's worthwhile to upgrade all the armor on all of your active heroes to about the same level rather than focusing on one hero or one type of armor.