Vibrato helps fretted notes sustain longer and gives them more presence. Why should the technique be reserved for the violin or cello? It's a great technique for the guitarist to add a bit of sparkle to the music.
Hopefully this video will give you a few pointers to make sight reading, and learning notes in the high positions, less scary.
Articulation and clarity are always a concern when playing the guitar as notes ring on. Here are some tips to avoid the music sounding muddy... not just stopping the notes at a rest, but stopping the open strings ringing beyond their written duration.
It is essential to add colour to the sound made on the guitar - the most straightforward way is to vary where along the string the right hand plucks. This variety creates interesting contrasts and brings the music to life. Julian Bream is a great inspiration to this approach.