Julia Driver argues that modesty essentially involves ignorance (underestimation) of one's self-worth. Intuitively, modesty is a virtue. So this would count against traditional accounts of virtue (as involving moral perception or an internal orientation towards the good), and in favour of her instrumental account. But there are reasons to doubt whether modesty essentially involves ignorance after all.
Driver suggests that an adequate account of modesty must meet at least two desiderata. Firstly, it must explain the oddity of asserting:
(1) I am modest.
Second, it must leave room for a distinction between genuine and false modesty; hence the account cannot be purely behavioural.
Driver's solution, as noted, is that modesty is a matter of systematically underestimating one's self-worth. Someone with coherent beliefs will cease to underestimate something once they become aware of their error, and so one cannot coherently affirm one's own modesty. And one can act with "false modesty" if one does not in fact have the false beliefs that one's seemingly modest behaviour suggests.
But I think there is a better solution, on which modesty is a kind of moral knowledge rather than personal ignorance. The modest person, I suggest, is one who has fully internalized the fact that they are just one person, surrounded by moral equals. The modest person is thus disposed not to dwell on her own achievements, or to see any reason to try to put herself forwards as 'superior'. If you really pressed her on it (say you rig things up so that an innocent person will be hurt unless she gives the correct answer), you might be able to get the modest person to admit - albeit with some hesitation - that she is indeed modest. So there's no real ignorance here. But in ordinary situations, the modest person will not consider this autobiographical fact particularly significant or worth dwelling on. They are disposed to attend to things more important than their own status, after all. And this suffices to explain the oddity of asserting (1).
As for the second desideratum, there's obviously a difference between genuinely internalizing this kind of moral perspective and merely acting as though one has (when in fact one feels the same enflamed amour propre as any egotist).
This characterization (or something along these lines) better captures my own concept of 'modesty', at least. But more importantly, it also seems to be a much more appealing character trait than the (merely instrumentally valuable) state of ignorance that Driver describes. More generally, for any proposed 'virtue of ignorance', I expect that it could be better understood as a virtue of salience, i.e. of attending to the right sorts of things -- things that actually merit attention.