The blade of Antarhak is ok ish, the mighty scroll is good, but highly limited by the army. They're only worth taking on a L4 because the chance of IFing with a L2 is only 1/36, and I would want to risk a miscast on my hiero for the sake of getting any of the LoN spells off IF, so realistically you need a second L4 with either light or death before the scroll becomes viable.
I've used Enkil's canopi for a while, but never saw a RiP spell so dropped it
The deathmask is the best of the bunch, but it is priced fairly and as you observed, limited by the army.
The cloak of dunes really isn't all that when you're unable to march, I'm interested to find out who you'd give it to as there doesn't seem to me to be much of a decent character build to put it on.
The undying banner is good, but suffers from being a bound spell, especially as the casket has a much more powerful bound spell that you want to cast every turn. Good for a tomb guard unit, but not much else, would be amazing if you could get it into a construct unit, but neither ushabs or necro knights can take magic banners and your BSB can't ride a serpent.
I think the other books do have useful items, I probably see O&G more favourably than you do by the sounds of it, I've run the last battle axe a few times on a savage Orc warboss and it turns him into a complete whirlwind of destruction, the stunty axe is fairly widely used as well. The star item of course is the shrunken head and the list is only really let down by its extensive collection of crap BSB only banners.
Empire looks to have the best MI list to date, the only item I don't see use for is the ring of Volans, even the AoMI is good for a WP/AL on foot and is underpriced compared to the equivalent common items. The griffon banner is yet another missed opportunity to allow a GS unit standard bearer to carry it, really don't get why they're so opposed to this. The problem is that in order to get your BSB decent protection without any magic items he needs to be on a bearded warhorse, which requires a very large unit of knights (4 ranks) to make proper use of it, I would add that while I've read some army lists on line of people fielding large units of knights, Ive never actually seen one in practice.