Low mortgage rates and falling home prices have yet to kick-start homebuyer demand as the spring buying season approaches, as many would-be homebuyers who are willing to risk the prospect of further price declines are unable to qualify for loans.Freddie Mac's weekly Primary Mortgage Market Survey showed rates at or near record lows for the week ending March 8, with rates on 30-year fixed-rate loans averaging 3.88 percent with an average of 0.8 point.That's down from 3.9 percent last week and 4.88 percent a year ago, and just a hair above the all-time low in records dating to 1971 of 3.87 percent seen during the first three weeks of February.Rates on 15-year fixed-rate loans -- a popular choice for refinancing -- averaged 3.13 percent with an average 0.8 point, down from 3.17 percent last w...