If the car has been thoroughly sorted out by an Acura technician, there should be no problem resulting in the flood damage - he would have been looking for as much work as possible at that time, and would have changed out any and everything that needed or would need to be in the future, because of the water.
Taking the car to another NSX specialist would be a great idea, and without mentioning the water damage, ask his opinion on what needs doing to the car to make it 100%. If he doesn't mention water damage, then the Acura technician has done his job properly 4 years ago. All electrical gremlins should have reared there ugly head by now, surely?
Offering around the $45k mark, any buyer would be getting a lot of car for the money.