Upload & Sell: Off
Brian, can you use the monitor portion of the iMac as an external monitor? The reason I ask is that awhile back, someone stated that you can access the iMac monitor as a separate monitor. If you can, that could be your external monitor for a new MBPro, assuming that the iMac monitor is decent quality (IPS panel).
If you can't use the iMac monitor as a stand-alone monitor, it highlights the problem with an all-in-one system. Once the "computer" portion becomes outdated, the entire system, including monitor becomes obsolete. With a discrete system, you can reuse the monitor. I've upgraded my computer twice while still using the same monitor.