It's funny too cause the Archmage robes are 1 of the few items in the game you can't surpass with self enchants.
You simply can't get that much benefit out of self enchanted robes... Not without resorting to enchant/alchemy BS at any rate. Best you can get I believe is like +60 Magicka (actually 10 more than it gives you) and +60% Magicka Regen.... (40% less)
The REAL gotcha though... is the -15% to ALL schools of magic. You can slap 2 25% school enchant's on... and even gear yourself to cast 2 schools for free... but if you want to be a PURE mage, who uses all their magic at their disposal, that -15% to ALL schools is a GREAT Boon and simply unachievable in any way shape or form on a single piece of equipment.
Besides the unenchanted robes simply being somewhat boring and plain, there's no good reason to use anything BUT the archmage robes anyways.... and actually, I don't really care for the hood much so I'm kinda a sad panda with my mage

I've actually taken to having her carry a set of "town clothes" which I'll be keeping up to date (obviously having to buy replacements to upgrade) with enchantments appropriate for in town (barter bonus, smithing/alchemy, carry weight, stamina, and maybe lockpicking with left over though prolly just a dedicated set of ring + gloves.