I've driven all over CA, at all times of the day and have never ever had any problems, while the vehicle was moving. As soon as you stop, it's always a good thing to check mirros and people who are moving towards you, especially at night.
During 7 years here, I've had 2 roadincidents where I've drawn my gun.
Both at night, in Managua, where I live so obviously that is where I would get in trouble. Main highways are "safe", and if we count the possibilty of beeing hit by other vehicles I'd say night driving is as safe as day driving safe since there are less driver during night. This is NOT valid during weekends as driving and drinking is a well practiced combination.
This is if you drive a car and have a cellphone, by bike you get into trouble for hitting a medium sized dog and it might take until sun-up for someone to help you....
All in all, the biggest risk of anything happening to you would be crashes.
No respect for bikers since they overtake sometimes even though they've seen you. Especially truck drivers, who on long straight seem to think that bikers can do with 1 m of space...
Tip, if you're following a vehicle, ALWAYS stay in the path of their tires.
If you follow behind, in the center and someting is on the road, you will hit it if you're close to the car.....ask me I've done it and almost fell with a semi-trailer 5 meters behind me.....
Keep your eyes open, in the cities try to position your bike so you always can take of if you feel something isn't right. If you do get robbed, especially in San Salvador or Guatemala city, stay really cool and co-operate.
A friend of mine was killed in Guatemala while car-jacked and he probably did some jerky movement or said something that wasn't appreciated. So, cool, no challenging eye contact, no smiles and no jerky movements if you do run into some tough guys. They DO kill for whatever reason in the above mentioned countries. I'd recommend knowing where you're going while in big cities. Gangs can kill for sports.
Honduras, a little more relaxed but still not supersafe and Nicaragua beeing the best place for not getting killed over some silly stuff. Here you can usually tell robbers from ordinary people because of their looks. These are the novice robbers or drug addicts. Tip 2, try not to stop at traffic lights (at night).....well, what I mean is if you see that the lights are going to switch, reduce speed early to roll slowly and sometimes don't stop at all.
If you really fell unsafe, cops probably wont bother stopping you at night, and if they do, not feeling safe can be a valid argument.
The tough guys are in the cities, and in smaller villages the only trouble would be drunk guys who need to compensate something. That would be an ordinary fight that might end as a robbery if you loose.
Americans are in some circles, in Nic, not appreciated. So if you are american, small villages and sandinistas might not be a good mix.
Well, that's my 2 cents and I hope it serves someone.