You haven't made any specific requirements in your request so I'll try and cover the general stuff. If you're looking for improved sonics with a small budget outlay get the 2Ce Signatures as Will suggests. This speaker is MUCH better than you probably think/expect. If you're looking for better movie sound for yourself get the 2Ce Sigs. Also, look at your source and processor as they will make huge differences in what you hear from any speaker. Subs are only going to improve the bass. So while this is sometimes worthwhile, you should only consider it if you already have done the L/R speaker upgrade IMHO.
No matter what, you should contact your Vandersteen dealer and talk to them about it. They can advise you better as they'll know more about your system, room and preferences.
Happy Holidays!