I really like the OP's suggestions, especially regarding the Griffon, Deamonslayer, and Sigismund banners.
And there are so many fluffy, good banner suggestions. I think most of them are a few (5-10) points too cheap, but by and large good.
Reworking the banners we have would satisfy me, however. Simple things like the Banner of valour(?): make it the banner of immune to panic and fear, same or small change in point cost.
Banner of re-roll rally becomes more expensive and re-roll panic and rally.
The most outrageous: Armywide rule: all detachments gain the benefit (or some more minor benefit) of their parent's banner if in close support.