So, given that they're pretty hard to find now days and your chances of getting the aspect you desire is 1 in 40- I'd like to make a small suggestion to towards a change in how the prisms work.
It wouldn't be too much of change, only that each prism can be used multiple times (up to about five probably), but each time it is used, the chance of success goes down as the DC for success goes up. My suggestion for ascending difficult class would be 15, 25, 35, 40, 50.
I like the idea.
Other things that might be worth considering - pity system, or breaking of blue hero items for prism scrap.
But suggestion in the first post sounds like if involves far less work than these, so I like it very much.