One of the major problems experienced at higher levels is the ridiculous amount of buffing that groups do and all that it entails in terms of bonus calculations, bonus stacking and what happens when dispelling magic is used and how it all interacts together. There are various ways to approach this problem, but here is one I haven't seen mentioned before:
We could create a few high level spells, each of which could provide the buffs of many of the lower level spells combined into one. This would significantly simplify the buffing process - casting probably only one or two spells instead of many and as such the number of buff combinations would decrease drastically with the advantage that buffs could be pre-calculated and take next to no time to calculate and adjudicate in-game and reduce bonus stacking calculations too. The interaction with dispel magic would also be simplified.
An extreme form of this idea would be to have only one high-level buff spell per type of magic. To make it less extreme, however, high level spells could be divided by function and type of magic. For example:
Divine Spells:
Combat/Physical Aspect - Bless, Bull's Strength, Bear's Endurance, Divine Power, Divine Strength, etc.
Pious/Mental Aspect - Eagle's Splendor, Owl's Wisdom, etc.
...
Needless to say, something similar could be done for arcane spells.
If we wanted to simplify it further, we could even ensure that the spells don't stack with other buff spells, but last 1 hour / level (thus improving the length of the adventuring day) and be very difficult to dispel. Perhaps these spells represent the limits of the infusion of magical power possible into an individual which could prevent the stacking. So Combat/Physical Aspect does not stack with Pious/Mental Aspect nor does it stack with any buffs that are part of Pious/Mental Aspect, etc. Note that this lack of stacking is not actually necessary, but I am just including it to expand the idea.
Although I don't actually favor doing this, taking this idea to the extreme, we could even make just one chain of buff spells per function and magic type (Least Combat Aspect, Lesser Combat Aspect, Combat Aspect, Greater Combat Aspect...) and thus solve stacking problems entirely. This is too extreme for my taste, but some groups may like it. Still, the creation of some high level buff spells subsuming the bonuses of multiple lower level buff spells is, I think, a good idea that could solve some very important high-level problems for some groups.