At 7th level he can smack something for 8d6 with his scorching ray, or catch a whole lot more than 2-3 critters in a hallway with a web...or keep the rogue who snuck up on him and just stabbed him in the back for 30 damage by casting invisibility on himself.
That much investment into spell focus conjuration, and even taking such a crappy feat as heighten spell says he's a 1-trick pony.
When it works, he's gonna he very effective...when it doesent work he's going to be practically useless.
Outsiders, dragons, constructs, powerful undead, oozes, and almost any monster that would normally have SR in the first place will all stand a reasonably good chance of saving against this spell.
I played a similar character once in 3.0 that was a transmutation specialist who'se signature spells were Blindness and Slow. He never took more than 1 fireball in a day and only kept a few other flashy spells on scrolls for emergencies. He had spellcasting prodigy, greater spell focus, used Spell enhancer and had fatespinner levels to even further boost the save DCs. Anything that was percieved to be a 'big smashy', or stealthy leather armor wearing type got slowed...Spell casters got blinded, and cannon fodder got squished by everyone else in the party. If it was really important to make a critter fail its save, I'd burn 3 pts of spin, cast spell enhancer, and IF it made it's save I could force it to re-roll once a day. At 9th level he could force a save vs blindness up to DC 27 and make you roll it twice. He was a ton of fun to play until we started fighting monsters that had ways to flee...We fought the SAME ogre magi 4 times, and usually soon after he'd blow us away with his Cone of Cold I would blind him. Since word of our tactics had then gotten out, every subsequent encounter was more difficult.
The next time around he brought creatures with scent to sniff me out while invisible and grapple me. The 3rd time, it was 'EVERYBODY kill that mage!'. The 4th time he was at our house polymorphed into one of our allies and had a ring of counterspells loaded with blindness, lol. We're all sitting in the living room talking, and suddenly he stands up and we all take a point black CoC to the face.
Anyhow, the point of the story was that the 1-trick pony has advantages and disadvantages...Once his primary tactic becomes known the bad guys will be more prepared. They'll stay more spread out, they'll create ways to flee. Have an low level hidden invisible spellcaster specifically to counterspell the glitterdust, something. Ready an action to rush behind a tapestry covering a concealed doorway if he casts glitterdust or something. Or just have a hiddne/invisible critter sneak up and grapple him/ interrupt his casting with a dagger to the spleen.