To make vertex selection based on it's valence (how many connected edges it has). In the Polygon menu SET goto Select > Select Using Constraints at the bottom of that menu.
Check 'Current and Next' then goto Geometry > Neighbours and set Min to 2 and Max to 2 and click activate. Start selecting vertices on your model, it'll select only the vertices which have 2 edge connections.
When you done either set Constrain to nothing or click Close and Reset. Don't forget to do this or you won't be able to select anything!