For several years I've used a Time Capsule drive to share slide show images for our home machines and to quickly pass files between users and machines. The lack of permission enforcement is a feature, not a bug.  (I believe the AirPort Extreme can do this as well.)
For much of this time I did not secure the shared disks, I just enabled Read/Write Guest access. This seemed to work, but it was unreliable. OS X seemed to drop the connection and it took some time to reestablish it with a connection dialog that defaulted to username/password. I had to switch to guest.
This has gotten worse recently, perhaps because my Time Capsule WiFi is dying . On a hunch I enabled "secure shared disks" and simply set a disk password:
I then connected from every machine and saved the password in the key chain. I left Guest as a read-only option.
Since doing that I think connections are much faster, and drops are much less frequent. I think sometimes OS X restores a dropped connection, whereas before it couldn't.
Wish I'd made that change years ago.
 It's rather hard to find out what operating system Apple uses with its Time Capsule and Extreme. I've read that at one time they used Wind River VxWorks, later NetBSD.
 Apple WiFi devices last longer than most, but even they seem to die after 3 years or so. I don't know why; I assume they die of overheating.