You could go T5s and VHOs no problem. We have come to find out its not really wattage per gallon but how you use the lighting you have. Although I think for what you have id go with at least 4-5watts per gallon minimum.

With that said in this hobby once something is used you rarely get anything close to what you may have paid for it. So basically if you paid $400 for your lights you might get lucky and get half of that back which you would turn around and spend on more lights anyways; so is it really worth selling?