You always want to make sure you're showing your innate curiosity, problem-solving, insight, etc. etc. You can't practice too much, but you can lose your ability to be creative and show interest.
I always advise people of the following "tricks" to make sure their cases don't seem robotic/flavorless
1) "Cover" framework titles. I.e. "Industry x Market" instead of Market, "Product X name" instead of "Product" or "Profitability" etc.etc.
2) Throw-in current facts: "I know x is currently happening in the world. So we may want to consider y". "I read something the other day about z, which applies in this way"
3) Show curiosity through responsiveness: "Oh, I had no idea the Korean cosmetics industry was so large." or "That's so interesting that x costs are so large. Makes sense now that I think about y"
Remember: A case is as much a behavioural as it is a case - always show that you're actually interested in the problem...it's going to be your 24/7 job after all!
Hope this helps.