I don't know about dumping the iMac, I can see using this in addition to the iMac. The iMac is just too powerful, and has a larger screen to give up on it totally imo.
My wife is about ready to throw her iMac out of the window unfortunately. I probably need to wipe it out and clean it. It has become slow as molasses. It is a 2009 model and had the hard drive recall. Lots of bad memories with this machine, and now the spinning beachball of death has been popping up since we've upgraded to Yosemite. If I had known, I would have never bothered - but I'm too into upgrading OS's especially when they are free :-D
I plan on giving her my 27" monitor that I use now with my Surface Pro 3 when I get my 30" monitor for my Surface Pro, that way she'll have a larger monitor. I'll get her a docking port eventually if she likes the Surface 3 enough to get a dedicated dock.
Like I said - for what she does, I don't think she uses 1/10th of the CPU power of the i7 in the iMac. Plus, I think having a SSD will impact her more than having a faster CPU.