My answer is to ask the question, particularly for home users, "Does the program do what you want it to do at the moment?"
If the answer is in the affirmative, I generally suggest that they can save money by continuing to use their existing software.
This approach often applies to more senior users whose needs are well satisfied by the "things they know". Also the learning curve involved is often a hassle for this particular group.
I often find that many senior citizens mainly use the internet to send email to their loved ones and are really not interested in the advanced features of MS Office.
Of course there are the exceptions, and in their cases, upgrading may well be a positive option.
Where a business is concerned, the collaborative features which are often improved in upgrade versions may well assist a company to more efficiently use programs in a multi-user environment.