You should buy a computer when you need it. If you can wait, wait.
New chips are expected from Intel in August, However, nobody knows how quickly they will make their way into Apple's machines, which machines will see them first, or how long Apple will wait to clear old inventory, etc.
I assume you have thought through why you want a mini for school. Reasons like allready having a monitor and keyboard or not being able to afford more. The mini is not as good a desktop machine as the iMac. And while it is not portable, it is easily stealable.
Best wishes