Quality over quantity!
One thing you should pay attention to is not to create spells are that are too specific to be of any help. Example: a skill that only cures poison. Then a skill that only cures paralysis. Then another skill that only cures silence, ad infinitum. This one is especially bad if you're making a game where all status effects are gone after a battle. Why not have a skill that cures all effects sans death instead? And then a single skill that revives? Much better.
If you have elemental spells it's alright to have multiple varities with different elements, but why not try to give them some secondary effects? For example, fire spells could have a 25%ish chance to inflict a Poison-type of effect, Ice could paralyze etc.
There's also another good way to make healing techs stay effective. Make them restore a set percentage of your max HP. For example, have a Cure spell that restores 25% of your max HP. That way, it will restore 25 HP when the max is 100 and 2500 when the max is 10'000 and so on. Having variants that restore a higher percentage is completely fine. Naturally, you can also do this with items, but that's no the point of this post.
Status effects are your friends
And don't just make the bosses immune to all of them, that's just boring. One way to work around this is to create two versions of the same status effect, one for regular enemies and one for bosses. Simply make the enemies immune to the boss version and vice versa. Who knows, maybe this can add a whole new layer to the gameplay of your own little creation?
So I hope this post was of at least some use. I really wanted to pass this advice down to fellow game makers, so don't disappoint me!