Like the title says, have separate enchanting methods for blue items and for purple items. We know blues are better early game, and purples have downsides that can be mitigated in endgame. Right now getting purples in early game feels awful and getting blues in late game feels unrewarding. Other games have no issue giving you downsides for stronger items when you personally choose to apply the effect. However here the choice is random and enchanting feels like it can brick your item at any try.
Suggestions:
Make blue enchanting available early, and purples become available after upgrading the magic shop.
or
Make enchanting blues a standard across all shop levels, but add a plagued currency that can purple any blue item at will.