I play MK7 all the time and I agree with the power-up system.
For example, this happens a lot; After about 10 seconds after you pass a set of Item Boxes, two CPU players at the back end get a Lightning Bolt and Blooper, and they use it at the EXACT SAME TIME, if it were a rare event, I wouldn't care, but it's just so predictable.
As for Spiny Shells, I have a little method for cheating the system. As soon as you see a Spiny Shell appear in a racer's item storage, stop/slow down and let 2nd Place take the lead for a few seconds and the Spiny Shell will hit them, and with the time it takes for them to recover, you can actually gain more distance between yourself and the rest of the pack. Though I have a rule that if you can't see any racers nearby on the Bottom Screen, just keep driving and make as much distance as you can for the next few seconds, because you can probably still keep your lead.
The trick to MK is using bad situations as an advantage to decieve your fellows.