Vegetable compost can help give many things to your soil. Vitamins, minerals, and such, the levels will be determined by where the veg was grown(what was the soil like? Rich in nutes, or did the grower add?), as wells type of veg you are composting. Adding soil will help to increase breakdown, IF it's not a sterile soilless mix. You can add beneficial microbes and fungals that will further increase availability of natural nutrition to plants when the compost is done.