Mystic Theurge is HIGHLY unoptimized. Being 3 caster levels (and 1.5 spell levels) behind the power curve hurts a lot, especially for your wizard spells. When everyone else is throwing Cloudkill, you're still using Fireballs.
The d4 hit dice and lack of turn undead progression make your cleric levels fairly useless, as well. Divine Metamagic is nice as mentioned above, but Persistent Spell (for warrior clerics) isn't so hot, and Quicken Spell isn't so great when you're so far behind on casting progression.
Finally, you have MAD: You need to keep pumping more than one casting stat (int AND wis).
Given the number of options out there to gain access to arcane or divine spells, I think you're far better off looking at PrCs that grant extra domains (Contemplative) that have the spells you want. If you're a wizard, there's feats that grant access to clerical domain spells. Or, be an archivist, which gains access to all spells. Either way, you're better off than if you do the Mystic Theurge route.
Even in Core, there are domains that offer most of the spells you'd ever want (Travel, for example, has the nice Teleport line as well as Fly and an awesome granted power), and a lot of cleric spells replicate what a wizard can do (except for direct damage, which doesn't kick in until Flamestrike shows up -- although this can be mitigated with the proper domain selections).