I did a lot of traveling in South America and it was a great way to see different countries. A lot of the buses were pretty luxurious with 180 degree reclining seats, meals and bus attendants to give your blankets and things. You could rest comfortably during the night trips. I also met some interesting people along the way. Some trips were horrible too, but at least I have the stories.
I probably wouldn’t do it in the US. Don’t know about other countries.
Can you actually extend the trip and stay at some hotels/hostels or something along the way? If the buses are comfortable, and you have the time and budget, i think it would be great to visit three different countries, enjoy the foods and sites, meet people along the way, and have that time by yourself to do whatever you want.