Nah the plates wouldn't work on the Evo and was very fitting for the MS3 as it was the repsonse that I typically got from those who thought it was just another little Mazda hatch.
I really consider the MS3 an excellent car and value especially when compared to the STI. The MS3 offers much better handling, steering feel and feedback, and I'm not convinced that sways, springs, struts/coilovers etc would fix the STI to make it better. The Evo is just so much more honed and focused right out of the box and was a very logical step from the MS3. Again it was driving the cars back to back is what did it for me. You can keep beating this arguement to death, arguing the merits of each on paper.
That being said, I do love the Subaru's looks and sound and do plan on picking up a 05-06 STI for a project car i a couple years.
I don't miss the MS3's ropey shifter, clutch, or torque steer, and so far don't miss the extra utility of the hatch. STI would be a decent choice if you felt like you absolutely had to have the utility of the hatch. I will give the STI this, that it's got an excellent gear box, with bolt action feel and engagement. The Evo's shifter isn't bad at all, and is a bit notchy but I actually really like it. Reminds me of my WRX when I had Kartboy shifter bushings.