IFR aircraft on visual approach to Runway XX experienced conflict with flight of two VFR aircraft on low approach to Runway XY; reporter alleged ATC's separation planning was flawed causing the event.

Narrative

ATC asked what type approach I was requesting. I advised; 'Request Visual XX'. Winds on the ATIS were less than 4 KTS; and ATIS was advising Runway's XY & XZ in use. ATC said; 'contact Tower' about 10NM out; I requested a Visual XX. Tower advised 'Plan Visual XX; contact Tower 4NM out'. At 4NM I contacted Tower with my altitude and they cleared me straight in Visual XX. Tower was also talking to a flight of 2 experimental aircraft doing a low approach on Runway XY. The flight of 2 confirmed their low approach and plans to depart straight out. The flight of 2 turned NORTH on a 'conflict' course with my IFR visual clearance for a straight in visual XX. Tower advised a flight of 2 experimental aircraft had turned north and were at 1;200 FT. That is pattern altitude and exactly where I was at. I immediately advised starting a decent below pattern altitude to 'avoid' the conflicting traffic; and started a decent to 1;000 FT. In the decent I located the flight of 2... BELOW ME AT 1;000 FT. I immediately climbed to avoid them. We came within 0.1NM of each other and 100' vertically. On the ground I contacted Tower by telephone and advised them of the near-miss. I also told them that I was the priority aircraft on an Instrument Clearance Visual XX. And told Tower they should have instructed the VFR experimental flight of 2 to depart straight out XY; which would have insured no-conflict. The tower operator told me the flight of 2 had told him they would depart 340; paralleling my inbound course of 160.