I go there every two years (check my galleries), so if you have a chance to go to any "feria" (street market similar to "farmers markets" in the US), don't miss it! Great spots to photograph people (ask permission first!).
San José is a large town... and it has its share of thieves. Just be aware of your surroundings.
Now, while the Olympus won't make you stand out, the Rolleiflex surely will... but if you can handle the attention, go for it. I took my Leicas last time, and had a blast with them.
Wides are useful, and if you run out of film, you'll find it easily in down town. There's a Kodak distributor near Club Union, which is the one I favor. The folks at DIMA (right next to the Teatro Nacional) are generally snobbish and that's why I stopped going there: overpriced gear and film. I never went to the Fuji distributor, but I did visit the Agfa one (which probably won't be there since Agfa folded). Development is expensive, so don't even think about it.
As for sightseeing, look for "San José Highlights" tours. The operators usually leave information in major hotels lobbies. It's a nice way to get around some nifty places near San José. I agree with egpj's advice about places in town. Eat well, sleep well and enjoy the pace! 🙂
And don't miss Cartago's cathedral! 🙂