I think it would be a very good idea to have a computer available for your guests. Luckily, not EVERYONE travels with tech devices.
How big is your hostel? Depending on how many guests you have, one computer would probably be enough. I ran a 43 bed hostel with 3 guest computers, and they were all constantly in use. I also ran a 50 bed hostel with 1 computer, and it rarely caused problems when people wanted to use it at the same time. Everyone just had to cut their facebook time short and join the rest of us for real face time instead.
The fact that there are internet cafes everywhere means that if someone is really desperate to use the one computer while someone else is on it, you can offer them an alternative nearby.