This questions raises all sorts of interesting issues. I'm going to limit my focus to the question of the relationship between morality and beauty and avoid any discussion of more general questions relating to truth and the value of art. But there's a wealth of good literature on the relation between morality and artistic value. See, for example, the essays in Jerrold Levinson (ed.), Aesthetics and Ethics, (Cambridge: CUP, 1998). But here are a few thoughts on beauty and morality.

It is true that we sometimes talk of immoral beliefs being ugly. We may also characterize immoral actions as ugly and moral ones as beautiful. And character assessment is sometimes made in terms of beauty and ugliness ; e.g., 'she has a beautiful soul'. But I'm tempted by the thought that these usages are metaphorical; that is, we are not really making aesthetic judgments--we are not literally ascribing beauty to these objects-- when we talk this way. Why? Well, beauty and ugliness in the paradigm cases are associated with perceptual experience. The most uncontroversial cases of literal judgments of beauty involve things that can be perceived. And the clearest cases in which we can be said to experience beauty are rooted in perceptual experience. For example, our experiences of the beauty of the sunset, the painting, the flower, etc. are based on our perception of those objects.

Our characterizations of immoral beliefs as being ugly doesn't seem to me to be based on their being able to be perceived. Neither perception nor perceivablity seem involved in our talk of their ugliness at all. But there does seem to be something appropriate or fitting in talking about immoral beliefs as ugly and virtuous people as having beautiful souls. This appropriateness is just the sort of thing one finds w/metaphorical language. So I suggest that immoral actions are only ugly in a metaphorical sense.

Now, it's also true that we characterize and experience proofs, theories, and literary works as beautiful, and that these judgments do not seem necessarily rooted in perception. The same seems true about non-perceptual imagery. But I don't think we should assume these characterizations are metaphorical. Note that experience is still really crucial in these cases. For example, the ordinary judgment that a proof is beautiful seems dependent on that proof being the object of someone's experience (typically your own). So too with respect to imagery. This seems very different from the immoral belief/action case. There it seems you might be tempted to call an action or belief ugly just on the basis of its description. Experience isn't required.

Upshot: I don't think the fact that we characterize immoral beliefs as ugly suggests that morality affects beauty, since I think these characterizations are metaphorical. In fact, a disturbing fact about human life and art is that beauty and morality often pull apart in dramatic ways. For example, some works of art are particularly dangerous because they present immoral ideas beautifully. Mary Devereaux makes a nice case for this in her paper "Beauty and Evil: the case of Leni Riefensthal's Triumph of the Will," in J. Levinson (ed.), Aesthetics and Ethics, (Cambridge: CUP, 1998).