As the original poster, I've been pleased and surprised by the number of thoughtful responses--and I certainly don't want to discourage further discourse on the subject. I've learned a lot, but one obvious conclusion is that there is no single best answer, and that there is no substitute for research. It probably makes the most sense to divide the whole hearing-aid question into two parts, one dealing with basic quality of life (i.e., conversational competence and the like) and the other dealing with the experience of live and recorded music; I've made a lot of compromises regarding the latter over the past few decades, but I can still make the case that music is actually part of my "quality of life" as well.
My impression is that the Costco experience, in terms of support and quality of offerings, would actually be a bit better than just saying 'Costco' might suggest. When I am in a position to do so, I will probably at least make some preliminary inquiries there. I suspect their offerings would probably be "good enough" as far as conversation and other basic functions are concerned. This discussion has provided a lot of helpful input with respect to the music question, certainly by introducing some names (e.g., Widex) that I might not otherwise have encountered during a routine search. By all means, carry on, and thanks again for all the responses so far.