I am surprised you like the devo8 over some spek radios. I prefered the dx7 and dx8 feel over the devo8 and devo8s. My devo12s had very nice sticks, but felt much cheaper and even with an amazing touchscreeen it didnt compare to my Jr which was about the same price. I guess everyone has a different feel for things
What I really like is some of the additions that walkera adds to their radios like touch and the recent addition the fpv monitor screens...what i dont like is their resell value and support.
On motors you are right blade replacements are too high but even Walkera seems to be ever raising their pricing too
As far as stability of Walkera i too found the minicp a much better heli than the mcpx, though walkera has nothing out to combat the nano or flys close to it. It will be interesting to see what they come out with down the line.
If you have a chance try comparing your 120d02s to a 130x. I really loved all my 120's when i first got them as nothing else came close too them.
On the Deviation firmware, while Walkera has some good radios that can be made to work with other brands I dont think any decent cllub would let you fly larger models with such a modified tx. For park flyers I dont see a problem unless you hurt someone else which probably is pretty unlikely...but be carefull flying that 250 size and above