Actually the streets layer has about two thirds of the total datsville brick count if I remember correctly 
The red crosses are 'file not found' indications. You can add additional search path to LDCad's config using prefs/LDraw/search...
You could also try playing with some of the rendering options in the same LDraw menu. For example turning off edges might help with the large models.
edit: using stipple transparency instead of alpha blending is probably the biggest save, because it's might become very cpu intensive if there are a lot of transparent parts in a model.
The red crosses are 'file not found' indications. You can add additional search path to LDCad's config using prefs/LDraw/search...
You could also try playing with some of the rendering options in the same LDraw menu. For example turning off edges might help with the large models.
edit: using stipple transparency instead of alpha blending is probably the biggest save, because it's might become very cpu intensive if there are a lot of transparent parts in a model.