I just did a little testing and I can confirm that putting more points into mind blast increases how often shadow master casts it.
Where's what I did:
-Made 2x chars in Hero Editor, 1x sin & 1x barb. Barb is going to be the target of my mind blasts
-Started off on sin with 0 pt's in mind blast. Then tested with 0 pts in mind blast and +7 from items. Then with 1 in mind blast. Then with 20. Then with 99.
-I recorded how many times shadow master cast mind blast compared to how many times she used other skills.
Here are the numbers:
Code
MB Level | MB's | Other Skills | Ratio
---------|------|--------------|------
0 | 0 | 18 | 0
0+7 | 0 | 10 | 0
1 | 1 | 17 | 0.059
20 | 10 | 12 | 0.833
99 | 18 | 6 | 3.0
I wasn't exactly precise about it, but nevertheless, it shows that more pts in mind blast make master cast it more.