NMAC AT A NON TWR ARPT CTAF BTWN 2 ARR ACFT; ONE OF WHICH IS NORDO TFC.

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DURING A ROUTINE ARR INTO COLUMBUS ARPT FROM THE E (OMAHA); CANCELED IFR FOR A VISUAL APCH INTO COLUMBUS 5 MI E OF ARPT. RPTED OVERHEAD ENTRY 500 FT ABOVE TPA (2900 FT) AND SEQUENCED INTO DOWNWIND LEG FOR RWY 32; BEHIND A PIPER LANCE TURNING FINAL. DURING ROLLOUT FROM BASE TO FINAL I NOTICED A YELLOW PIPER CUB WITH 2 PEOPLE IN IT SLIGHTLY HIGHER AND R OF MY R WING. I CONTINUED FOR APCH TO LNDG AND LANDED WITHOUT INCIDENT (2100 FT ALT). LATER; IN DISCUSSION WITH THE CUB'S PAX; THE VISIBLY SHAKEN PAX SAID THE PLT NEVER SAW OUR ACFT ON L BASE (PIPER CHIEFTAIN PA31-350). HE STATED THEY WERE SIGHT-SEEING ALONG THE PLATTE RIVER AT LOW ALT. BECAUSE IT WAS DUSK; THE PLT OF THE CUB (NO ELECTRICAL OR RADIO) DECIDED TO LAND STRAIGHT-IN ON RWY 32; DROP OFF HIS PAX; AND DEPART FOR HOME FIELD. CAUSE AND CONTRIBUTING FACTORS: 1) POOR/REDUCED VISIBILITY AND NEAR DUSK; 2) IMPROPER PATTERN ENTRY BY THE PIPER CUB; 3) FAILURE OF BOTH PLTS TO SEE AND AVOID; AND 4) LACK OF RADIO COMS. CORRECTIVE ACTIONS: 1) BETTER VISUAL SCANNING FOR TFC; AT UNCTLED ARPTS IN PARTICULAR; 2) STANDARD PATTERN ENTRY BY ALL PLTS AT ALL TIMES DURING VFR FLT AND IFR FLT WHEN PRACTICAL; AND 4) RECOGNIZE COMPLACENCY WHEN OPERATING OFF HOME BASE ARPT. STAY ALERT.