See if you guys notice any feeling of lateral movement in the rear end. Particularly when going over uneven road like turning into a driveway with the dip or something similar that shifts the vehicle weight from side to side. I noticed this on my 400 when I put 25mm spacers on. Not like any noise but more of a feeling transfered to the driver. Spacers will change the alignment slightly too.

 

How would adding spacers affect alignment if the alignment is correct and spacers were installed correctly and flush with original axle?

 

Yes, spacers affect the camber and / or toe alignment. How much is debatable. By pushing the tire out angles change.

 

Technically there might be subtle changes in the geometry of the wheels fitment, but not even close enough that leads to needing an alignment.

You are extending the length of the horizontal axis of the fitment, and depending on the brand/type of spacers you will have some changes along the vertical axis. But is it enough for you to need an alignment? No.