That is good to know about the name change --- when we were there in March it was still guest services. Concierge does sound more upscale, I guess. I agree the "level" of service should be the same at all three "levels" of resorts...I just haven't had much luck with them getting a hard to get ressie. It seems when you pay to stay concierge that for some reason they tend to have more influence or "magic" in getting those hard to get ressies.
With guest services (oops concierge) at the resorts, in the past, it seems my odds of getting somethng I want when calling dining from my room are about the same since we both dial the same number. The upside of doing it in the room is that I don't have to wait in line to have them do it. I know at the moderates sometimes the line can be rather long, depending on the time of day, etc. I have not stayed at values so not sure about there.
The other option is simply to try to plan an early or late meal where you want to eat ... not at a popular time ...then drop in and see what the wait time is ... Keep in mind that often people do not show up for their ARs and that opens up a table. While I always try to call there have been times when we didn't make our reservations and didn't call. Much of this, though, depends on the time of year you are going, the size of crowds, etc.