I agree with you that Volume measures both buys and sells, I would add that while it is NOT an indicator of rising pps, it can be a VERY GOOD indicator as to what is going on during a rising run.
If you use volume along with a few other indicators during a run, you can actually see your exit point coming and get out before it tops out and drops like a stone to the bottom of the lake. When you see the pps continuing to increase and volume starts becoming less and less, that is a good indicator that interest is starting to go away and that you might consider taking some or all profits off the table.
I have been using this for a while now, and yes it is true I might leave a few marks on the table, but when the stock rolls over and drops and goes well past where I sold, that more than makes up for it. IMO