You have a nice bike. $1000 new is going to buy you a entry level road bike with Sora/Tiagra. $1000 used may get you a lightly used newer bike with 105 or Ultegra (or SRAM or Campy) components.
I had a bike with CX2 back when the brand was called Retroshift. They are nice for what they are but I'd rather have STI levers. The CX2 is for a double chain ring so you would need to get a new crankset and probably front deraileur or get the Audax model shifters and use friction shifting.
It's going to be hard to find 7 speed sti levers. If you are patient you can probably get a 105 group for $250 on ebay used or you can buy new for $425-500. Then figure $150 if you plan on having a shop do all the work for you.