I'm playing with enbseries dll's for some time now, different games but mostly WOx and I've also noticed that setting for /Shadows and /SSAO dont make any visual difference (plus quite big performance hit with SSAO, but this might be specific to ATI card as I'm using 4870x2). I'll stick to Bloom and Colour Correction, these alone can be spectacular. As for too dark try play with /DarkeningAmountDay -try lowering that value for brighter "shadows".
Also I'm using GTA Vice City v0.075c3 version of dll's (after lots of testing these seems to be most stable/fast for me).
my ini file plus some shots
enbseriesini.zip