igd - Go back to that spot and dig every target - even the iron.
As far upgrading your equipment, we all have our opinions. I'm a Minelab guy. Had good luck with my (now 7 years old) Explorer II on beaches as well as in the mineralized soil of Culpeper County, VA. I suggest you start by picking your price range, then read reviews on machines in that range. There is tons of info out on the net. The bottom line is - any detector can find targets if you know how to use it and where to look.
Good luck.
DCMatt