"MSE has similar anti-spyware capabilities compared to Norton anti-virus or Kaspersky anti-virus, but not as good as the Internet Security packages from the same companies."

Take a look at the feature chart from Norton:

http://www.symantec.com/norton/antivirus -> Compare Related Products

You will find that there are no features differences between Norton Internet Security and Norton Antivirus when it comes to antispyware.  Therefore looking strictly in terms of antispyware capabilities, there is no gains going from NA to NIS.  (You may be interested in other features of NIS that is not in NA, but that's beyond the scope of this discusion.)

Take another example:  Avast.

http://www.avast.com/en-ca/free-antivirus-download#tab3

Again, there is no gain going from Avast Antivirus (free) vs. Avast Internet Security when it comes to antispyware protection, other than faster (they probably means more frequent) updates of signatures. 

I have been using Avast Free for years, unti MSE comes to the scene.