I found the upgrade from Server 13 to Server 14 to be quite straightforward, with one gotcha:
If you have a split deployment for WebDirect, AND if the Master machine has multiple network interfaces, disable all except the one you want the WebDirect connection to use before doing the deployment.
Good tip on the network interfaces.
I went and did it last night, and I am very happy with the results. Better performance, better resource efficiency, and better experience in Web Direct. No showstoppers, only minor friction.
There is a new warning for Web Direct users that the administrator needs to install a custom certificate. In the documentation, this sounds like an optional step, but with a large red warning dialog appearing to users about it, this step is probably now required. Worthwhile anyway, so not a big deal, but a surprise.
But my database files and RC data folders in Data/Databases were immediately picked up when I moved them from the old installation into the new installation, so that went very smoothly. I reconfigured LDAP, schedules, notifications, and admin options, and everything worked on the first try.
I guess I should have known that if it was a rougher process, this forum would be thick with complaints. But I can report positively that it went very well.