Believe that you NA is running in a very good condition. If you think you can sell you NA with that much to get a cheaper TT, then go for it, but make sure you don't have to dump lot of $$$ for repair! If not, I would keep driving your NA till you get some decent income and get a new Z after 2003 :-) Well, still love my TT even new Z debute.
So, do what you can AFFORD, or you will be sorry to get into debt!