When using add-on's to enhance perception of value, it is important that the add-on be something fairly expensive.?

That statement is False.
You could easily used cheap adds-on in order to obtain the additional value that you want.
Many companies even use other unsold products that they manufacture in order to create the value added perception from the customers in order to maximize their profit.

False. The add-on must be something fairly inexpensive, usually tacked onto something expensive: e.g. laptop protection for $20 on a $600 laptop