We are very aware of the importance of Int for Holy Paladins, however we have just not found any suitable proof that 30 int warrants a score rating of 15, however we have found proof that 63 spellpower is a more beneficial enchant.
Using a standard Holy Paladin template on lootrank shows a score of:
Mighty Spellpower - 142.38
Major Intelligence - 67.5
Rawr - the number crunching program also lists Mighty spellpower above Major Int in both burst and prolonged healing simulations by a value of over 20% in the standard model we tested.
Also, a quick check through the paladins of some of the top guilds and I couldn't find one that used 30 int over the spellpower enchant. The main problem is, that even though Int is incredibly useful for holy paladins, this is a BC enchant and its itemization reflects that, if Blizz release a new LK version of this enchant, I'm sure it will easily be the top.
Anyway, if you find some interesting article or some theorycrafting to backup your statement, that would be great but for now we have to score it according to the credible research we have found, and yes we do put a great deal of time and effort considering all enchants on every class and spec.