if you are going to full adjustable arms, then YES, you need the lock out kit
the stock eccentric bolts are a point of failure - they slip over time and wear. As you are adjusting camber/toe/caster through the arms, you no longer need that adjustment point, hence the "lock out" of those bolts
I am curious how SPL is changing the springs. Fitment wise, it's easy - throw away the progressive springs, swap in some 65mm ID swifts. But are those now linear? won't that throw off the valving? I mean, SPL knows more than me, i trust their setup. Just wondering what they're doing here
They sell KW so presumably they will know how to make stuff work with their own parts
EOD it won't be anything you can notice, i suppose
EDIT:
Don't stop the lockout kit and mid-link
Get the traction arm too
Your alignment tech will thank you. All 3 arms work in conjunction and affect alignment.
Whatever spring you get, buy some Swift thrust washer/thrust sheets:
http://swiftsprings.wpengine.com/products/misc/
Save yourself from squeaking and popping noises
SPL can order these for you