If you don't have Keep-on-covers on the speedplay cleats, or Speedplay's walkable covers... what gets ground down is the metal plate and especially the screw heads.Most of my friends use Speedplay. I've been using them for close to 10 years. I like the larger platform of the Speedplay cleats...and its also two sided. Since they are not made of plastic...the Speedplay cleats don't tend break when they start to wear down. One of the reasons Shimano is more common is because they cost less. The Speedplay costs a bit more. I'm using the Zero with the stainless spindles.
But speedplay is very maintenance intensive, and especially if you accidently walk on a patch of dirt, it's going to interfere with clipping in. Yes, it's easy to put some dry-lube (like Finish Line Dry) on the cleats, and the annual pushing new grease (good ole Supertech Marine Grade grease) through the spindle bearings isn't that hard, just messy.