Basically this explanation doesn't predict variation in male traits at all, but that choosiness has no cost to females, because they are hard wired to prefer certain types of males. When population mean for male trait reaches the selective optimum, selection will favour reduction in variance, but this may simply be difficult to acheive, especially if a lot of genes with pleiotropic effects are involved. Again a constraint on optimisation. Thus genetic variance in male trait is maintained at equilibrium by recurrent mutations, which females select against. Again the optimum is to eliminate mutation, but this cannot normally be done for any trait.
Male traits are an indicator of viability.
Females choose 'handicapped' males with expensive traits, because only healthy males can afford the cost of making these traits. The optimum is for all males to be equally healthy, but this can't be achieved if health is determined by something that changes fast, like parasite genotypes, because of the high population size and rapid generation time of parasites. In my opinion this is not completely true. Oh I dont think we have any good evidence for this at all, except Hert's paper on eggspots, which are colour, of course, vary within a species, and are selected by females. They are definitely under sexual selection.