The spell costs exactly as much as creating an unslotted, custom magic item, yes, and even with CL shenanigans doesn't necessarily allow for extremely high-end items. What's more, it's a permanent duration spell. Regardless of your CL, if you get hit with an MDJ then these bonuses are gone. If you spent the time to craft the magic items, then you'd at least get a save.
So yeah, you really need to make it Supernatural with Dweomerkeeper in order to make it at all worthwhile. That should take care of the SR issue as well.