When you say ruin the Cat5, do you mean ruin the Cat5 rating of 100MPS? From what I understand (not personal experience, but 2nd & 3rd hand sources) you can ruin the cable's ability to transmit at these higher speeds, but unless it is certified, you'll rarely know it.
Now if we're talking cat5 for phone use, I'd say yes, you're being overly cautious. if you did happen to short a pair together, you have 3 more to choose from.
