Another serious problem is short term thinking... Your existing IT system may be slow, unreliable, clunky, but it limps along and the staff are familiar with it... If you replace it, users will have to get used to the new system, a new way of working and probably a new set of bugs to work around. A new system may cost a lot to implement, may result in a long period of reduced efficiency as staff get used to it etc.
I still consider this thinking to be very short term as well. At some point, the upgrade will have to happen; either on your own time table (now or soon) or on the system's time table (when it breaks and isn't recoverable.) I'm personally of the mind - even though I make good coin when it happens the bad way - to put a replacement plan into action before the devices hit the crapper. Replacing it after it breaks still causes the same headaches and is more of an expense due to the unexpectedness of the upgrade.