It is scary how many people commit their marketing spend purely based on their own perception of their market rather than on tangible research/analysis evidence.
When it comes to splitting your budget between traditional and digital activity then it would be impossible to say without more knowledge of the market you are in and your customers purchasing habits. However the beauty of the digital medium is its flexibility and versatility, allowing you to execute and analyse sampling activity both quickly and inexpensively. This should enable you to compare ROI data against historic data from traditional activity (if you have such data available to you).
Good luck.