Your current fix for the druid will have his power level higher than the rest of the party, depending on optimization levels, but within tolerances. Don't give him any more buffs.
I completely ignore the monster manuals except as a source of ideas. I write all the monsters and enemies for my games from scratch, but that's because that's easy for me, if it wasn't i'd probably customize monster chassises. I ignore CR and just eyeball their effective strength(s). I just find it easier than fucking around with CR and whatnot.
For example, against a party of;
3rd level warblade
3rd level witch w/ familar
3rd level crossbow rogue w/ a cursed greatsword that he had to use
3rd level healbot cleric
and an absentee 3rd level summoner wizard
I put together this encounter as a boss fight/finale;
2 x 6 1st and 2nd level warriors
1 x 3rd level expert/2nd level mob boss w/ crossbow with exploding bolts
1 x 7th level Artificer with armour that gave him fast climbing and 6 natural attacks and +16 total grapple mod and constrict, and a potion cocktail powerup injection
1 x 6th level necromancer w/ Magic Jar as a contingency
1 x Corpse Beast, i.e. modified lesser flesh golem being used as a mount by the necromancer
1 x 3rd level magewright w/ a hover platform controlled with UMD checks
1 x cache of repeat-fire blackpowder weapons in a storeroom (could be used by either side, although the warriors know that they are there and the PCs don't)
1 x group of reinforcements in the form of; 1 2nd level expert, 1 warrior1/expert1, 3 warrior 1's (and the party's wizard)
The PCs nearly died so many times, but they managed to pull through. That was a too-hard encounter on my part, but it gives you an idea of the way I design encounters. The fight was in an underground room with two levels, a staircase, a giant elven crystal monolith artifact, control consoles, storerooms, a secret passage, and with the enemies not knowing the party was there.
I've also put parties up against;
A huge cistern with dropaway floor and wall hangings that are animated objects with levels in ninja who can use each other as weapons with the only exit blocked by an endless flaming stairs trap
Magma elementals living in a pool of lava using heat to create 'tunnels' of magma to magmaswim through and attack from the walls and floor
One hundred goblin archers, a goblin swordsage, 3 themed orc warblades, an orc sorcsage, a hezrou blackguard riding a dire rhino, and an orc shaman specializing in illusions
A single spear fighter using sidestep, robilar's gambit, reach, elbow and knee knives, elusive target, evasion and mettle to basically stymie the party
5 young adult dragons of each of the chromatic colours. Against a level 5 party.
Siege weapon and bow using goblins in a covered gulch with a rideby attack horde of wolf riders and blindfighting raging barbarian 1 ogres with mindsight Blue goblins sitting on their heads, while trained bat swarms slowly bleed the PCs and many crude traps slow their advance (against a CR 12 party)
EDIT: Oh, and against a CR 15 party (quite weak though)
300 heavily armoured fighter 3 dwarves (200 tower shield cover with teamwork and phalanx fighting feats infantry, 100 poison wind grenadiers and arbalestiers)
6 groups of themed level 10 dwarven heroes (alchemist with bombs, wizard with wands, rapier fighter axe fighter spear fighter wings of cover wings of flurry sorc Force Missile Mage wizard rogues rangers druids) (they used the alchemist's corpse as a bomb and blew up about ~50 dwarves and one dwarven hero group)
8 dwarves riding some MMIII monster dog with swallow whole and 200hp and a fear gaze or something
8 dwarven siege cannon
a dwarven sapper team
some dwarven field medics and ward-based cleric/runesmiths
1 runescarred berserker with antimagic field (Slayer)(epic duel between the hengeyokai frenzied berserker warshaper and this guy)
in a fairly narrow underground stone corridor spiral staircase thing the party was resting on (4th or 5th encounter of the day).