Cyber-Cafe Business: Still Viable?

Yes, it is. In major cities such as Abuja, Lagos and P.H alot of people have atleast a 56k connection, however,  there are some that don't. I'D probably be good for you to get a connection in neighbouring cities/towns/villages that aren't really yet fully incapsulated in the computing world

NEPA and the preponderance of cafes in an area determine the viability.

Most places in PH charge =N=100 per hour.

In Yenagoa, most cafes charge =N=150 per hour and people still flock there.

I recommend Yenagoa as a good place to set up a cafe.