When to upgrade, your opinion?

I'm working on a presentation for a water/waste water trade show dealing with SCADA systems and controls. One of the topics I am going to cover is upgrading software whether it be Wonderware, Citect, Indusoft, Etc. versus maybe just spending money on development time. I'm not looking for a right or wrong answer just basically an open discussion to help end users decide where to best spend their money. I have been on some applications where the money would have been best spent on standardizing graphics, adding easier ways to access trending and alarm functions, or just basic housekeeping like removing out of service equipment from screens.

We have a policy of no dead code ... there by keeping the graphics (and control system) up to date.

As for SCADA ... we will install latest software once the first service pack is released.