This is a question arising from Brad's recent post about text assets.
Depending on how you read Brad's post there are between 100 and 200 spells in Elemental (10 per side or 20 per side). To put this in context Master of Magic had 210 spells, a variety which was one of the reasons it was so popular.
How many of MOM spells were actually used ? Were Cloak of Fear and Flying Fortress fun ? (hint - neither spell...actually works !). How about Subversion ? The spell worked against you. Instead of worsening other wizards' diplomatic relations, it worsened their relations... with you ! If I remember correctly, Resurrect spell was notorious for corrupting savegame files !
Ooooooow.. but I LOVE arbitrary comparisons with Master of Magic! 
On a general note though I can't imagine a situation where having more spells in the game would ever decrease the amount of fun I was going to have playing it, so the more the merrier I say. Having said that if I was a developer and had to come up with, code and balance them all I might feel differently
You can't imagine ? Let me come up with such a situation. No-brainers. The concept isn't new. Sometimes one option (spell, unit etc) is soo much better than other than the other is made obsolete. Examples from MOM:
War Bears vs Hell Hounds (War bears are often beaten by a unit of swordsmen. They're weaker than hell hounds AND cost more. Optimal play dictates to never use War Bears if you also have Hell Hounds).
No-brainers are options which remove other options, especially in a marginally competitive environment. In multiplayer, expect any ridiculously poor options to never get used.
How about Cracks Call ? It was the 25 mana spell that had 25% chance to outright kill any non-flying corporeal unit, no matter what. It was basically coin flipping and it could either totally nuke your huge investment or do nothing. Do you think having more spells *like this* contributes to fun ?
My point: Having more options is useless if not all are viable. It's actually dead code ! It can even be detrimental to the gameplay.