I think lower concentrations should work accurately. I've done quantitative assays RNA inputs for RT's as low as 15ng/sample. That was diluted 1:10 and used at a final concnetration of 0.27ng of RT in the QPCR rxn. I think it also depends on your detection equipment. The ABI 7900 is quite sensitive. I'm not familiar with the lightcycler.

no doubt that these assays can be expensive. Scale down strategies for RNA can really conserve precious RNA such as clinical samples (priceless!)

I use 10 ng cDNA per qPCR reaction with good results. Have you tried making serial dilutions of your cDNA to determine your quantiative range? I have found that I can get acceptable Ct values down to .01 ng cDNA.