4 wheel drive is a must if you want to handle all adverse situations at the ramp.
Most 2 wheel drive veh. are front wheel drive (BMW is one of the few exceptions I think), when properly rigged the hitch will take up at least 10~15% weight of the boat+trailer(say 200~300lbs), and this will reduce the front wheel traction on the ramp...for steep, dirt ramps that could be challenging when you are trying to pull the rig out of water...(some may have seen fat guys lying on the front hood of the veh, trying to increase wheel traction)
For veh. that are not towing ready, in the long run you may need to consider enhancing the rear suspensions and the addition of gear box cooler