Well reasoned Ben , I contemplated getting 4 of these , one for each of my Grandchildren.
You "could" try just one at first...you know, just to be quite certain the model has the child friendly characteristics you seek?
I "may" have ulterior motives as there "may" be a number of members that would enjoy seeing what the "SPS effect" has on an engine born in china....just saying 
I think you may have done all the improvements that can be had on these (I may copy many of your idea's) , I did think that I would ask each Grandchild what color they would each individually want for their engine.