Solo touring is fantastic. You do what *you* want at that very moment, no matter what other people might think you should do - no negotiating, no waiting, no making someone else wait. You can ride as much or as little as you want, eat when and where you want, stop to add or remove layers when it's comfortable to you, w/o asking someone else to wait. Stop and see/do the things that interest *you*, not someone else.
Do you like museums? Skate parks? Antique shops? Wall mart? Roller coasters? Dive bars? Upscale espresso? Gas station coffee? KFC? All-organic live raw vegan food? Forests? Beaches? Sun? Shade? What about your friend, what does s/he like... is it the same?
Also... there is nothing like touring alone to increase your self-reliance. This carries over into the rest of your life. Touring solo is a great life teacher. There are huge psychological rewards.
EVERYONE wants to talk to you. You don't have to be lonely if you are even a little bit friendly. The bike is a great conversation starter.
That said, it's great to tour with a real friend, especially if you like the same sorts of stuff, ride around the same milages per day, and get along well. But there are a lot of compromises. Touring is a strenous physical activity, and you and your friend will learn more about each other than you may wish. Whatever a person's core qualities are, they will appear on tour. So if you go with a friend, you should know them well. If you go with a stranger, you should be prepared to compromise, keep your mouth shut if you are unhappy, and go off on your own if needed.
Pacific Coast is a great tour, have a blast!
Anna