I think most of these changes are a good idea. I will miss Summoners and I think that Archmages' limit should be upped to at least 5, but simplifying the spell system seems like a smart idea.
However, the new priests seem far too weak. The point of Priests before was that they had a diverse selection of spells that were useful in several different situations, making them an effective alternative to archmages. Overspecializing priests and limiting them to two generic spells and two unique spells greatly limits their usefulness. I vastly prefer the older priests, and think that while the new priests are a good idea to an extent, they need more spell variety.
In a possibly related note, if you get rid of Gaurdian Vines and Lifespark I will hate you forever.

Not really, but these are two of my favorite spells. Both are permanent summons that serve a use other than straight combat (The medic 3 on the Lifespark has saved my ass SO many times), which are sorely lacking in FfH. If anything, there should be MORE non-combat summons instead of fewer.
I also agree with the idea one person had of increasing the number of spells per sphere to 4. Admittedly this would probably require adding a bunch more questionably useful spells, but it has the added plus of forcing you to choose between specializing a caster in one or two spheres, or branching out to cover a bunch of low level spells. And this gives an opportunity to add some more interesting summons (For example, the incredibly potent Spellstaff could be tier 4, and Enchantment could get a tier 2 or 3 spell that summons a Mud Golem, giving any civ access to a powerful worker.
If a system of four spells per sphere is implemented, it should definately NOT require a fourth level of caster. Instead, I'd recommend doing it in one of two ways: A) Tier 3 spells are in general only a bit more powerful than tier 2 spells, while tier 4 spells are VERY powerful. In this case, allow Mages to cast both tier 2 and 3 spells, and only Archmages to cast tier 4. B) Tier 3 spells are quite a bit more powerful than tier 2 spells, but tier 4 spells are only slightly more powerful (or just simply different in purpose) than tier 3 spells. In this case, allow Archmages to cast both tier 3 and 4 spells.
Anyway, there's my opinion on the whole matter.