Normally, I weigh in on the side of individual privacy... but
I consider this information to be relatively public by nature and there are considerable benefits to having this type of system in place.
Resolving amber alerts faster, Locating stolen vehicles faster, Improved efficiency of local governments, etc...
Balancing the need for individual privacy/rights with protecting the individual rights of other citizens, while operating within a limited budget is a tricky thing. The need to avoid the "slippery slope" is great, and the loss of individual privacy should always be considered a great cost, but a cost-benefit analysis should be done. The following should be kept in mind though:
1.) Individual privacy is not priceless.
(How much Individual Privacy have some people freely given up just to use facebook?)
2.) How does the cost of hiding information like X impact the individual rights of others?
City budget cuts are pretty common these days and often translate to fewer police. I would argue that a system like this could improve efficiency and help lessen the impact of cuts like these.
I believe the information should be purged when it is older than 2 months in order to help limit the scope of the system to a near-time discovery tool as oppose to a long-term tracking mechanism.