Ok before I post I'd like you all to know my Helian spellcaster is only lvl 5, and my druid/cleric/mage is only rating of about 7 in each of those. So I have no experience really with them. However my 72 Lunus did use all the breezes (only the top tier available) and also the debuff/buff spells whenever she needed.
But, my point is pretty much the same as Justa's. Now, I HATE for all mmos to be a clone of each other, I particularly hate that most of the big ones (WoW, EQ2, LotRO) are all basically the same game with different skins. But even in those, they all require mana for spells (or rage for warriors etc etc, some form of finite energy at least). Those that aren't clones, e.g. UO also insists that everyone has mana to cast a spell (note abilities are different of course). Virtually every rpg/mmorpg/arpg has some form of finite resource that stops you basically spamming over and over again.
I think the nearest to Hz is Sacred, where you can have 5 'Combat Arts' equipped at once. They can be of two categories, spell or just combat art. They all have individual cooldowns. So say you have two spells, firebolt and icebolt, with cooldowns of 3 and 4 seconds respectively. Cast firebolt, both will go to a cooldown of 3 seconds. If you cast the icebolt first, the firebolt would take the 3 seconds cooldown and the icebolt will take 4 seconds cooldown.
Anyhoo, my point is they should leave it as it is, but perhaps look at fixing some of the cooldowns if they're a bit extreme. In WoW you only use a lower tier if it is still effective BUT MORE MANA EFFICIENT. Since we don't have mana, perhaps the "essential" spells can have a lower cooldown if it does prove 'gamebreaking'.