I decided to go ahead and use the command line utility (shp2pgsql) to import my .shp file. Since I was able to get it working without too much trouble and a little Googling around I wanted to share this possible solution for anyone else who just wants to import a .shp file into Postgres and didn't want to deal with the hassle of trying to get pgadmin's GUI geospatial data importer. To import a shapefile here is the command (of course you need both Postgres and Postgis installed, first):
shp2pgsql -I -s <SRID> <PATH/TO/SHAPEFILE> <SCHEMA>.<DBTABLE> | psql -d <DATABASE>
And here's the OpenGeo docs explaining each of the above parameters:
The command parameters are:
<SRID>
Spatial reference identifier
<PATH/TO/SHAPEFILE>
Full path to the shapefile (such as C:\MyData\roads\roads.shp)
<SCHEMA>
Target schema where the new table will be created
<DBTABLE>
New database table to be created (usually the same name as the source shapefile)
<DATABASE>
Target database where the table will be created
So just as an example, here was my command:
shp2pgsql -I -s 3857 ~/Downloads/MoGeospatialData/MO_2012_Senate_Districts.shp public.geospatial-data | psql -p 5432 -d vetting-geospatial
If you're not sure where to get the SRID just go here and upload your .prj file and use the topmost match it generates: http://prj2epsg.org/search
And for a comprehensive explanation of this CLI and importing data in general, just check out this great documentation from OpenGeo: http://suite.opengeo.org/docs/dataadmin/pgGettingStarted/shp2pgsql.html
I hope this helps someone!