Being an almost theoretical concern at this point I am not putting this on mantis yet, but..
I think that the range for a spell tier might need to be increased from 5 levels to 8-10. there are other solutions to my concern but that strikes me as the simplest solution for the time being
Why? Lets take an example, loosely based on my current character.
I am Level 45
I use Ball Lightning IX
I use Fireball IX
I use Forest Rage IX
I use Energy Pulse IX
At this point I should start trying to acquire Level 10 gems to upgrade my spells, except this requires, One Ruby, One Opal, One Jade and One Citrine (other ingredients aside).
The odds are I shall level up twice getting each gem, so before I even get three gems I should already being trying to acquire Level 11 Spells.
My options are continue getting the Level 10 gems knowing that by the time I have acquired them they will be out of date, or go straight for the level 11 versions, and create a situation where I have to level spells alternately otherwise they get left behind.
Now currently there aren't many spells in the game, so it's not as big an issue as it could be, but by the time you add utility spells, defensive spells and whatever else the devs have coming for us into the mix you are going to need a lot of gems to upgrade with not really much time to get them.