I was thinking that getting all Venezuela or all Colombia would give you an extra bonus on top of continent bonus.
This is an example. Red is impassable borders, mountains and rivers.

In the Purple area of Venezuela, 20 (Sucre) connects to 18 (Nueva Esparta) which also connects to something on the other side, like 23 (Vargas).
The continent bonus calculator gave:
Colombia:
Caribbean (Pink) 4
Andean (Brown) 9
Pacific (Teal) 3
Orinoco (Yellow) 5
Amazonian (Light Green) 5
Venezuela:
Zulia (Lime) 4
Coastal Range (Purple) 5
Andean (Dark Blue) 3
Llanos (Orange) 6
Guayana (Dark Green) 3
(I think these bonuses are unbalanced and a little inflated but it's just a rough estimate)
Alternatively, I could join some of the regions in Venezuela and Colombia.... Dark Blue in Vzla and Brown in Col. could be join into a pan-Andean region. Light Green in Col and Dark Green in Vzla could be join into a pan-Amazonian region. Orange in Vzla and Yellow in Colombia could be joined into a Plains region. This would make bonuses for holding all Venezuela or all Colombia more interesting.
Colombian regions taken from:
http://en.wikipedia.org/wiki/File:Regionsofcolombia.png
Venezuelan regions taken from:
http://ecoportal6.tripod.com/natural-regions-map.jpg