How to read a Property value
This article is relevant for all .Net products
Mixing up Attributes and Properties is a common misinterpretation.
An Attribute is some data, bound to a certain node class (Object, ObjectType,Variable, VariableType, ReferenceType, DataType and View). The available Attribues are fixed, thus they cannot be extended to contain additional data.
Properties have almost the same syntactical meaning as Attributes, but Properties are completely different nodes (of the node class Variable) with own Attributes. The Property node is referenced from the parent node via a HasProperty reference.
To read a Property value, you have to get the NodeId of that Property (e.g. via TranslateBrowsePathsToNodeIds) and perform a read on the Value Attribute.