Hm. I still think that 'exploitable, but only if you really tried to' is better than acting against the spell description (AKA the developers intent, since HLAs were already done 90% before my time anyway). I'm against playing at being the police.
Seems reasonable to me. Though it seems easy to stumble on the exploit by accident, I certainly didn't noticed it for several years using Refinements HLA's as a player with any number of mages and thieves (I admit that this may be in part because I don't take Scribe Scroll early in the HLA picks, and also that I use my scrolls that I scribe soon after creation in 95% of cases). I only discovered it while testing the kit I've been making which used a similar opcode.
As for Union, the immunity to spell failure seems like a good idea to me.
EDIT: You could also try to take advantage of opcode 280 and 281 to use a set wild magic effect to generate some interesting "metamagic" bonuses to casting. On the other hand this would break the wildmage's surging, allow a major abuse to Reckless Dweomer, and the effects may prove to be just too powerful for an ability with one hour duration (you could have spells cast at double level..., which is better than +5 but really doesn't do a lot except for dispel chances). If the WM were a class rather than a kit you could use eff files to fake normal WM behavior (i.e. 5% of the rounds the aura is in affect the WM doesn't get the surge table set, but uses a random surge table). Also this would allow union to protect against the WM zones in WK. I'm not even that sure this will work, but I plan on experimenting with using 280 and 281 to make an HLA and will see, how it goes.
-Acheron/Starcrunch