Collective bargaining is most useful when the 'little guy' has few options, or the switching costs are very high. Consumers seem to do well when purchasing other types of insurance, and I think they'd do well to get rid of the principal agent problem (if they can keep the tax benefits).

I think the biggest problems with employer-provided benefits come at the 'employment transients' (i.e. the time just after leaving jobs and while getting new ones).