Plan to remove benefit for failing leves?

[normalforce]

You know I may just sound like a broken record but adding some sort of incentive to completing leves aside from the extra SP would go miles in convincing players to finish the lev.

Complete 1000 regional leves: Here have a cool Triple Triad card!

Oh, yes please. Triple Triad <3!

And something like what you mentioned would make a nice addition to the achievement system:

Completed 50% unique levequests - get small bonus (+% att, +%def, or +% SP gained, more monsters spawned, etc. only during leve battles)
Completed 75% unique levequests - get another bonus
...
Completed X number of total leves... (1000, 2000, 5000, 10,000 etc.)
...

Or grant SP bonuses to the number of leves done in a 108 hours period. Call it levechaining. 6 completed leves and SP gain improves by 10%. 8 completed leves, +15% SP bonus. 22 and 24 leves cap the SP bonus to 50%.