Re-using quality tape is not an issue at all. When I was younger I did this quite often because I was always tinkering with my setup and couldn't afford new tape every time I changed something.

As a personal rule I replace tape once a year. If I need to pull the tape during the year and it is not overly cut or worn then I will re-use it (sticky or not). The sticky tape is not needed to hold bar tape in place.

I also keep at least 2 boxes of Cinelli cork tape in my shop at all times...just in case. I love the tape, it lasts forever, and I can usually find it aleast 2 or 3 times a year under $10.

I know that this advice is probably not in jive with my OCP membership, so I'll temper this by saying "reuse it if it is the only tape you have that matches, and be sure to carry extra new tape in both mathcing and complimentary colors - change when dirty"