I went to El Salvador (and Guatemala) in 1993. I really enjoyed this trip. It was very low budget. El Salvador is a really cheap place to visit, probably only Nicaragua is cheaper. When I was there, there was military everywhere, but I felt pretty safe.
El Salvador has several volcanos you can climb. The one I climbed is Izalco (also called El Faro del Pacifico - The lighthouse of the Pacific). Take water with you because it gets hot up there!
Salvadoreņos are also known as guanacos. It's a local nickname and I don't recommend using it with people you don't know. Salvadoreņos are mixed Indian and Spanish. You won't find typical Indian dress here like you can in Guatemala.
A really yummy food to try is Pupusas. These are corn meal based with beans or cheese inside. I always bought food from street vendors because it was so cheap and I never had problems.