So a thought occurred to me... with the new Parry system granting Shield AC, it may be possible to revamp the Shield spell so that it grants Shield AC instead of Deflection AC, by tying it into that system, as per the SRD? (See:
http://www.d20srd.org/srd/spells/shield.htm )
Assuming it is technically feasible... I think there are a number of positive effects to this idea.
I know people often complain that Enchanted Helmets are weak -- precisely because the AC type they grant, Deflection AC, is eclipsed by two level 1 spells -- Shield and Shield of Faith. In general, this idea makes high Deflection AC a little rarer -- and therefore it makes spells items that grant +1, +2 and +3 Deflection AC that much more valuable.
It diversifies spells a bit more; currently, spells to boost Deflection AC and Natural AC are more powerful and more common. Meanwhile, there are a few spells and items that can boost your Shield AC, but they are less common. Getting +4 Shield AC currently is limited to high level Clerics and greater magical varnishes (and enchanted shields against certain types of damage); all those are high level options.
I don't think this would count as a nerf -- it would still make Shield a very useful and popular spell, especially at low levels, when you're simply not going to have another source of Shield AC that powerful. But I think in terms of quality of life and diversity of play, it would make the game more interesting.