I've suggested some fairly general anti-feat-tax house rules before.
In essence:
- All Expertise, the Robust Defenses feat, and all Epic X defense feats are banned. Instead, PC's get a free +1 boost to attacks and non-AC defenses at levels 5,15 and 25. Non-AC defenses get an additional +1 bonus at level 1.
- At levels 4,8,14,18,24,28 players raise all ability scores by 1 rather than choosing from just 2.
The idea here being that NAD's are too low even at level 1; and further as levels rise, the "lowest" NAD suffers disproportionately since it corresponds to an unraised ability score. It's not just the NAD, however: racial powers and other non implement/weapon powers also fall behind the curve, as do skills. Aligned builds that have a primary/secondary ability of the same defense pose additional problems, and split-primary builds are almost entirely unworkable. Then there's light armor builds without an Int or Dex primary or secondary. Almost all of these things suggest that the real problem isn't the NAD scaling, it's ability score scaling.
In some sense, D&D inherently causes imbalance since ability scores diverge as levels rise. Fixing this is a fairly simple, general solution: it fixes NADs, odd light armor builds, MAD dependent builds, racial powers, skill divergence, etc.
A slight tweak allows for easy implementation in the character builder too:
- Ban Expertise etc. Instead of raising attack bonuses/defenses, decrease monster defenses by 1 at levels 5/15/25, and monster attacks vs. NADs at levels 1/5/15/25.
- require players to forgo the normal +1 to two stats levelling process, and instead house rule all abilities to rise by one. The character builder will happily let you enter any ability score, so people can continue to use it.
Note that these changes effective grant people 2-3 extra feats throughout the PC's lifetime and make them slightly more flexible. In general this means you'll want to make monsters a little meaner. Any DM will need to adapt his monster repertoire to the overall level of party optimization, but a good starting point is to consider all monsters to be 1 level lower (i.e. make em 1 level more powerful) but remove 1 hp/level (2 for elites, 4 for solos).
These changes avoid punishing players that optimize poorly - in normal D&D, such players may forgo expertise (this leads to problematic intra-party imbalances), or have poor ability score distributions, or raise scores inefficiently at levels with choice. These choices are all false opportunities for personalization: to the novice they look like choices, yet one option purely superior. Those kind of choices simply make it easy for casual players to shoot themselves in the foot; and as far as I can remember I've seen that happen
in every single party I've played in so far - there's always someone who violates these basic charop principles and ends up with a less powerful character for no good reason. In a game as combat-focused as 4e is, that's a problem.
In particular, it's worth noting that the suggestion to raise NAD's by 1 at level 1 is not frivolous; the average monster AC attack is just 1.5 higher than the average monster NAD attack, yet even at level one PC NADs are commonly at least 3 lower on average, usually 4 lower on average, and 5 lower on average some defenders - and that's at first level, before NAD decay and the various feat-related means of increasing AC that NADs don't have.