Spence,
Of course it would be preferable to have a separate set of all chips, but if not practical, I would at least consider having separate high-denomination chips for the different events. Having different 5K, 25K, 100K tournament chips is probably much more important than having different 25s or 100s, especially if it is much easier to obtain the higher-denomination chips in one type of event than another (whether because of differences in buy-in, or people just start out with those big chips in one event earlier than in others) thus giving cheaters that much more of an incentive to pocket chips from one event for use in another.
K