higher dpi = beter quality.
The more one scans, one will be able to notice patterns or settings which result in better or worse results.
When you say you can't read staff lines, what exactly is the problem? To blurry, pixelated, small? You know in Adobe you can expand or shrink to fit page when you print. This is good for stretching the print to fill the page instead of having so much blank space on the boarders. However, if the scan was at too low a resolution printing big could result in pixelation. In this case it may help to print smaller to get crisper lines.