I posted a topic on shards a few days ago and added some things in about this. Even if you cannot change the type of shard, still giving you some bonus on a spell based on every shard you own. Here's the post:
https://forums.elementalgame.com/415609
As for the spells you mention being weak and not scalable (such as heal), you could even do something similar to, once again, Master of Magic. For basic spell such as firebolt, you have your basic spell along with a slider to increase its power by using extra mana. Basically, the game is set up where spell research, mana generated per turn and skill (the amount of mana you can use per battle or per turn if you're casting a spell that requires lots of mana) are all adjustable by sliders. Going into a big battle and need lots of mana available to cast? Drop the slider on research and mana generation to have tons available, etc. It was a very good system.
Anyway, the slider idea for basic spells is great, because at lower levels you skill isn't very high, so you can't buff your spells. But as you grow more powerful and capture more shards, you can add serious buffs to spells. Thus, shards are THE things to grab in this game--I've had some nasty battles for them.
I do totally agree... a heal spell that heals 8 HP when, at upper levels, you taking multiples of that in damage makes the spell useless.
