Going to replace front and rear shock absorbers soon with KYB. So, is it recommended to change springs at the same time? I don't deal with salt/snow, so that's not an issue.

This is a G35X. I am going to replace the upper mounts and insulators for the fronts, as I believe they're noisy, but I noticed the bottoms of the front end springs have a thin layer of rubber around the last 360 degrees of spring, to separate them from the lower strut spring mount surface. It does not appear that this has worn through to create any metal on metal action, but it has started to loosen/peel towards the edges.

So, what to do? Just reuse for now, and if problems become noticeable, replace later? (This is the AWD, so removal is fairly simple. )

Also, the steering/handling/suspension all feels very loose now, although it's pretty straight/stable/quiet even at 80 MPH. Mostly, I notice looseness at <30 MPH and in parking lots/speed bumps. I have resolved most of the clanking noises due to sway bar end links, compression rod bushings, sway bar mount insulators, etc., but the car just seems sloppy still. Could this merely be due to the ineffective dampening of shocks with 140K miles on them? Anyone else have similar problems with higher mileage?

 

Unless you plan on lowering it I wouldn't call it necessary. Your springs should still be fine at that mileage. You damping should just be dependent on your shocks.