If people feel like they have all they need, then that burden falls on you. It is your job to market yourself and what you can offer. Typically I can market higher packages by selling the importance of bridals and engagements, a second shooter, and sometimes even Albums. I never try to sell something to a client that they really don't need, nor try to convince them to get something they really don't want - but as a professional it is my job to encourage them to get something that they would be missing out on otherwise - and explain to them clearly, why in the long run, it is important.
A lot has to do with the naming of packages and making the lowest package feel like the bare minimum, and just "getting by". While some want the bare minimum - most realize this is a once in a lifetime event and are ok with spending more, as long as you can explain the importance of spending more and justify it for them. It then is you job after to deliver as promised, exceed expectations, deliver excellent service, educate your clients along the way and make them feel secure about the decision they made. If you can do this, you will be successful.