Will blown in insulation help in this situation?
I'd blow cellulose into the 10' space, from above.  I'd worry about moisture and rodent problems with cellulose between the old tar &amp; gravel and the rafters.  The tar &amp; gravel makes for a moisture barrier you don't really want.

Check your venting in this attic space, and consider a humidity controlled fan.
You probably have K&amp;T wiring in the 10' space, if so see https://diy.stackexchange.com/a/20279/5960