Don't know if many other than us would be interested, but we have many thousands cases in our data base. We actually have a chart that breaks down averages in just about everything.
It shows different categories of players, ie. Top 100 ranked, top 5 round draft picks, Top 500 ranked, DI commits, overall average of everyone, etc.
It includes info for velocity, different pitches, 60 yard dash, pop times, velocities from every position, hitting grades, power grades, fielding grades, H-1 times, PG Grades, and more. It can even break down by height weight or even by state or region or include everyone.
For example it would show RHP or LHP peak velocity averages for freshman, soph, Jr, and seniors for each category.
Example, Average peak velocity of all Jr RHP that were eventually ranked top 100 was 89... average as a senior was 92. In pitchers drafted in the first rd, the average was 94, but still 89 as a junior.
So based on the data we have (thousands of pitchers) you could say the average velocity gain between jr and sr year is 3 MPH.
Problem is the averages mean very little to an individual. First rounders averaged 5 mph increase.
I doubt if anyone has a database of player information this large. So the numbers actually do mean something to us. Not sure if they would mean that much to anyone else.