I would like to use the <Rate> tag against any 'counter' based metric family as this is more in line with the statistics practices within our Statistics organisation.
In addition the <Unit> tag should allow additional values. eg PerSecond.
Having counter metrics plot points simply showing as a value rather than rate is bad practice as the values are highly dependant you having a perfect environment where data collection is timely. eg every data point is collected at the same interval. In the real world that is not going to be the case. A 5 min polling interval may vary between 5 min and 5 min 15 sec between plots so you aren't really comparing values over the same length of time.
A rate however is the value / the actual time period (usually in seconds) so the plot points are always going to be based on the same time interval (average seconds) even if the was a variance in the interval between data collections.