I'm in the same debate with myself right now. I'm looking into buying a garmin 162 or 176 and when I demo'd the units at boat-us, both with and without bluechart software, I noticed a world of difference.
If I'm going the GPS route I've found that in my waters, I would not want to be without the bluechart info. It is tremendously more detailed and displays nearly everything that would be found on the corresponding NOAA official charts.
Without bluechart installed, I noticed a whole variety of channels and islands that were not represented. The big decision maker for me was also the depth info. Very important in our area.