Sorry for the late reply. You pose an interesting idea, I'll definitely have to look into this, though I do want to let the new changes in the new Demo sit for a while. I think using the "Burst" spell gets around the RNG element of the combo idea, since the spell cast will be the same as long as the combination of spells remains the same. Also, in the newer spell casting system is that you can swap which card you want to lead your Arcana chain using the num keys. This is important because the combination "Burst" spell is based on the element of the card you have leading your chain.
Going with your combo idea, in the new demo's spell system I have reduced the time between casting spells as well as having each card in your Arcana Chain have their own cool downs, which overall increases the frequency and speed you can cast. As for the spell levels, ideally as you play through the game, you will find cards that are of higher level, that do more damage and may have a similar effect to the lower level cards you are using. I kind of want to avoid locking people into paths, but there is the affinities mechanic I am currently working with in which the player picks 3 elements essentially, and by doing it increases the rate of seeing cards of those elements when exploring. Anyways thanks for the comment, I appreciate it! :3