It is important do detach main melody from chords when they are just accompaniment as they are in this piece (sometimes this might not be the case).
For a crescendo, sometimes I would raise only melody, sometimes both, varies with musical intention, but it is important melody is up, so generally I wouldn't raise accompaniment as much, but generally would raise them a bit. (by raising I mean raising volume, or playing louder).
There are other useful ways to detach chords from melody which might give you more room to the guitar limited dynamic range, allowing you to play both but keeping the detachment. You could do this through articulation (eg, accompaniment non-legato or very rhythmically even against a legato melody or with more fluctuation and agogics) or through tone color (brighter vs darker or fuller vs thinner sound, through adjusting finger angle, amount of nail, degree of fingertip flexion etc.). Those techniques increase a lot the difficulty of execution, but they add a lot of richness to the musical result.