First, let me congratulate you on the big uplift that v5.8.4 is over previous versions!

I was pretty excited about the Site and Device copy options, but was disappointed to learn that it was strictly limited by device model.  One of the biggest uses for this configuration copy would be as clients upgrade, ie a bigger router, faster AP, larger POE switch. 

I have verified that I cannot use a SG2208 as a config source for a SG2210P, nor can I use an EAP-235wall a source for an EAP-615wall.  I know there are two EXTRA ports in the first case and I would have been happy to just have the first 8 copied over, you can imagine how exciting a 24 port switch getting copied to a 48port would be in a larger and growing installation.  I see no reason whatsoever though not to copy configs between APs, either because the new units being added are upgraded, or because you are upgrading the old ones.  Even if there are tweaks that are different between them (like the EAP615 supports fast roaming and the EAP-235 doesn't....fine, leave that at the default...you've still done 90% of the work for us).