C172 VFR ARR TO FXE EXPERIENCED NMAC WITH UNREPORTED TFC ENTERING SAME DOWNWIND FOR RWY 8.

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I WAS ON A TRAINING FLT WITH A STUDENT PLT. THIS WAS HER 2ND FLT AND THE STUDENT WAS FLYING. WE WERE RETURNING TO THE ARPT FROM NW AND WERE ADVISED TO ENTER FROM THE N; RPT 2 MI N OF THE FIELD AND ENTER L DOWNWIND FOR RWY 8. OUR ACFT DOES NOT HAVE TIS OR TFC ALERT SYS; SO EXTRA CARE MUST BE USED TO SCAN FOR TFC. WE WERE APPROX 2 MI NW OF THE FIELD HDG SE WHEN A TWIN CESSNA APPEARED FROM OUR 10 O'CLOCK POS FLYING SBOUND; MAKING A R TURN IN FRONT OF US TO JOIN L DOWNWIND FOR RWY 8 AT FXE. THE TFC APPEARED TO BE AS CLOSE AS 100 FT IN FRONT OF US AND FAST MOVING TO OUR R. WHEN I SAW THE TFC I DID TAKE OVER CTLS AND PULLED UP WITH A L TURN AVOIDING THE TURNING TFC (BUT GOT A LIGHT HIT OF HIS WAKE TURB) AND RPTED THE NEAR COLLISION WITH THE TWIN TO THE TWR. WE DID NOT GET A PARTICULAR ACKNOWLEDGEMENT TO OUR RPT AT THIS POINT. WE WERE THEN TOLD TO FOLLOW THE TWIN AND WERE CLRED TO LAND ON RWY 8. ONCE ON THE GND I DID RECEIVE THE TAIL NUMBER TO THE OTHER ACFT. THE REST OF THE FLT WENT UNEVENTFULLY. I FOUND THAT THERE CAN NEVER BE ENOUGH VIGILANCE MAINTAINED ARRIVING TO AND DEPARTING FROM ARPTS; ESPECIALLY AN ARPT SUCH AS FXE; WHICH IS IN THE MIDST OF SEVERAL AIRSPACES AND OTHER ARPTS. THIS MAKES THE SPACE CROWDED AND CAUSES ALL TFC TO USE MOSTLY SAME QUADRANTS TO ENTER AND EXIT THE TFC PATTERN. ALSO; THE MIX OF TFC IS QUITE BROAD; FROM STUDENT PLTS TO CPR JETS AND PVT FLTS ALONG WITH HELI TFC ALL BLENDED TOGETHER.