Thornblade and Shillelagh spell

[Jodro]

For blightcaster, does Shillelagh work on Thornblades and if so how it works? Whats the damage output?
Besides that does shillelagh spell has any important use on higher levels? Aren't the weapon enchantments way more important?

And just a suggestion for future updates. If shilleagh spell works on thornblade I would personally prefer being able to magically create a Quarterstaff too.

EDIT: It says thornblade gets improved every 5 caster levels, improved how? Whats the old and new damage?