I have been very tempted by the iMac, and if it gets USB C and TB3 in the next update it would be even more attractive, but it is mighty expensive. To prevent myself from doing that I bought a 27" ASUS IPS panel to go with my 2011 MacBook Pro that is almost always pugged into an external monitor. We'll see if that works. I will be tempted by a new Mimi if it has Iris Pro. A dGPU would be even better, but it seems unlikely.
I was feeling the same way and it is expensive and I also said I would never own an AIO.
I had to make a decision wether to stick with OS X or go strictly Windows because there will probably not be another quad core Mini in my opinion.
But when you break the iMac down your getting a desktop quad core with a dedicated GPU with a top of the line 5K panel and the ability to upgrade your own ram. The only way to justify the price of an iMac is to price it out as separate items and the price does not seem that unreasonable ( I tell myself).
You can easily dress a Mini out to iMac prices nowadays without quad core processor, dedicated graphics and a 5K panel.