I agree with the above. I've had a base Retina iMac for 6 months now(with 24 GB aftermarket RAM) and i'm extremely satisfied with it once they release an update for Yosemite to fix some lag issues on the Imac. Assuming you shop smart and don't spend much money it's not going to lose that much value(I'd be looking to spend under $2500 including tax and shipping)*hint the fusion drive model is actually very snappy so don't be scared to get one if you see a really good deal*. The biggest value hit this would take would be if Apple released a complete redesign in October which isn't likely.
Agreed. I just added a MacBook to the family, but my Retina iMac with Fusion drive is a fantastic machine.