I am building four leaping arches. I am using 10' x 1" Pex tubes. I am pretty much following Matt Johnson's model but I will use all 10' with the bases 75" apart. Each tube will have a 5 meter 60/20 pixel strip. so I will probably wind up cutting about 20 nodes from each strip. Now to drive the arches I have two Raspberry Pi3 ($30 each) with a Falcon PiCap each (another $30 each) and one 12 vdc, 400 watt power supply ($29) to power both Pi/PiCaps and the 4 strips. So total cost $190 Can you do this with a single $180 E682 plus the same power supply (add $29)...sure. Plus the E382 will give you 12 outlets to control other stuff, all be it you will probably need to add a second power supply. Or maybe use an Falcon F4V2 at $110 which is $20 less than my two Pi/PiCap controllers. Choices choices.
With respect to "piling up" as many pixels as I can on a single controller port and using power injection I have my own personal design philosophy. When I can, I try to stay away from setting up my system where I have to use power injection. I realize that sometimes you just can't avoid it. But if I have choice between power injection and additional direct connection to a controller I choose the latter. Maybe I am old school when you did not have a choice.
Bottom line here is we have options, there are pros and cons on every option we choose. Most times is a matter of personal preference and product availability or product delivery times.