Is it possible to read or import Attribute files?

No, but following workarounds are available:
- From the context menu of Lists use 'Copy cells' and 'Paste cells' to transfer attribute values between models.
- File -> Read additionally -> Network (with an INPX file)
In the dialog 'Read additionally' uncheck alle Network object types which are not needed and use the settings 'Conflict avoidance' = 'None' and 'Conflict handling' = 'Overwrite object'.