A lot of blue mage abilities are locked behind dungeons. These dungeons cannot be soloed and requires you to get people to run it with you defeating the point of a solo class. I suggest one of the following.
A. Set it up so you can que into older content once you hit a minimum number of spells.
B. Make a blue mage que that will allow others to help blue mages out while getting rewards/tomes for doing so.
C. Make blue mages able to solo content by increasing their damage and health.
D. Make blue mages able to do all conted nt including new savage content. You would have to do some balancing (x amount of tier 1 spells, x amount of tier 2) and so on but i believe its totally possible.
I know you are raising the level cas p to 60 shortly but thats a stopgap as we will get the same problem when we hit 60