I would try to overwhelm the opponent's magic with our own.
The empire can field a lot of level 4s, and all of them can have a total +5 dispel bonus. I don't think any other army can do that (but yeah, they can field immortal dragons so...).
Maybe you can go with 3 lvl 4, to have a good board coverage (given 24" dispel range), every one of them with the wizard familiar, one may also have a lore familiar, so he chooses spells. I'd also take battle magic so you can cast offensively too, casting fireballs and pillars with 3 mages might be actually strong.
I wouldn't invest in an altar, tho. It's too damn expensive for the little it does and really has no role since its leadership 8 doesn't make it a good general. If it had Ld 9, maybe.