A potential 20 percent drop in origination volume in 2006 may spur more mortgage banking consolidation in 2006, but experts don’t expect to see a merger frenzy develop this year. Buying a mid-tier mortgage lender may be a good way to maintain volume and revenue in a tightening market, said Craig Focardi, a research director at TowerGroup. But mortgage company acquisitions will increase only “slightly” over the tepid pace of the past few years, he…