Any air will make SOME difference as long as there is a delta t (difference in temperature between the cooling medium and the thing to be cooled) and this delta t is crucial. The fluids being cooled in the radiators etc is close to 100deg so even if the ambient air is 40deg there is a 60 degree delta. Also, you mentioned fins, imagine the total surface area of those fins and compare it to the surface area of your pump. Also, how much air does a huge range rover displace? Many hundreds of times more than a computer fan will.
As to driving, I regularly drive from/to Northern Italy from Czech which is about an 8 hour drive and never a problem. Under normal driving, your compressor shouldn't be running very often anyway.
If your pump is overheating, something is wrong and needs fixing. Extra ventilation is just trying to mask the problem and it's a safe bet that when it finally lets go, it will be at the most inopportune moment.