Uhh, Don't worry about the "'newer'" minis noisedude, yours is slow in an absolute sense. You are correct about the cause of your performance bottleneck. A quick and painless solution would be to connect an SSD by using an external USB 3.0 housing. With two Macs it should be simple work to download a copy of OS X and install it on the SSD. Then your 2012 i7 will fly.
I do not understand why the speed of newer minis matters in your case. Some 2014s have faster storage than yours ever will and some may be as slow or even slower. It does not matter. Your Slow 2012 i7 is a silicon based oxymoron. You already have 16GB of RAM. Get fast noisedude. Get fast quick!