So how "good" are my cleric buffs? Well at level 19, I have Spirit Armor (+14 AC), Daring (+8 AC, +115 HP), and Symbol of Transal (+34-73 HP) for a total of +22 AC and +188 HP. At level 24 when I get Bravery (+9 AC +140 HP) which replaces Daring and Symbol of Ryltan (+158 HP) which replaces Symbol of Transal I'll be putting a total of +23 AC and +298 HP on a player. For casters of that level, that probably comes close to doubling their HP and about 50% improvement of their AC (it's a smaller effect on tanks who have better armor than casters).

Now, how does a druid's spell compare? Well at 24 they get Skin Like Steel which adds 10-11 AC and 74-100 HP. Frankly, if you have a 19+ cleric in the group (and the cleric has the mana to spare)... ask before casting SLS on anyone (including yourself) because it overwrites Daring (because SLS has a higher AC value).