Honestly, I think the CL boost is the strongest feature of Archmage. 5th level is a rather ****ty level of spells (I think a lot of 4th level spells are STRONGER than some of the 5ths listed), and the +1 CL gives you lots of boosts. My level 14 Archmage has a CL of 14 +2 from Archmage + 1 from Craft Magic Tatoo + 1 from Orange IWIN Stone = 18. At 15, he'll be able to hit CL20 GMWs. His spells are already tough to dispel. His EBT Grapple check is rediculous. He overcomes nearly all SR with Arcane Mastery + advanced CL. Unlike Clerics, Wizards don't have NEARLY as many free ways to increase their CL. Archmage is one of them.

Again, I might be missing something here, but I've found that to be certainly one of the more useful High Arcana's in practical use.