You are correct in assuming that the sparklines for a group are an average over the resources in the group (over 8 hr period) and the text value being the 'last' value in collection interval.
Probably a better representation is multi-line graph showing all resources individually. However, since there is already a couple paths to multi-line charts now and our focus is on RHQ.next() it will probably remain in its current form.
Thanks Mike - I kind of figured they were averages, just wanted to make sure
I think bars are fine as long as there are averages - we already have line graphs available and I rarely click into the "see more" section anyway.