You can also add additional vector-specific tweaks to your vector.ini file. In the past, I think increasing contrast, gamma, and beam width seemed to give more pleasing results (at least on my monitor) but I haven't played with these settings in recent versions of MAME so experiment away...
#
# CORE SCREEN OPTIONS
#
brightness 1.0
contrast 1.0
gamma 1.0
#
# CORE VECTOR OPTIONS
#
beam_width_min 1.0
beam_width_max 1.0
beam_intensity_weight 0
flicker 0