This is pretty common. A Client gets their first tattoo on there arm thinking that this will be the only tattoo they will ever get, only to find out a year or two down the road their arm still looks very empty.
This is actually my cuzin Brad. He got this soldier's cross before being deployed. We took the space around it and created a background with more depth than the solid cross had to offer, but not making the background more important than the cross itself. I also thickened up the outline on the old tattoo to straighten it out more than it was. When adding on to old tattoos, it's important to make sure that the end result looks natural. Adding the light rays helps to tie these two images together.