Just for my opinion, there is no such average volume as you said. There are so many alt coins, their prices vary so large.
But if you compare the volume in several months or years, with the different prices for one alt coin itself, you can see or predict some trends of price. The volume is important of course.
Yes, trading volume is not important in a matter of time more important than community acceptance of crypto coins being traded. In my experience, the crypto has a trading volume of over 100 BTC in 24 hours is very good for you to choose.