Can someone remind me what putting ranks in a Gathering skill does besides act as a countdown to the next Tier? Is it only gathering speed? Does it improve the amount that can be drawn from a single node?
According to Lee, the number of items you get depend on skill (not level directly).
It may be so that higher (skill or level) increase the potential value of what you find, but I'm not entirely sure about that.
Speed of harvest, and chance of any given line from the node's list turning up.
At miner 9? (dwarf, 110%), I find very few mineral nodes with only one item. Even then, usually multiple quantities of that item. At least every fourth or fifth node has 4-6 resources in it with multiples of some items.