well better quality scans you can obtain by scanning good photos or whatever the thing is not to have smudges or etc 'cause the scanner doesn't remove that. and also try scanning them at a higher resolution and then messing with the scans in...(you guessed it!) photoshop. nevertheless search for a scanner that has a high scaning resolution (dpi) and that supports many many colors. for example i use a Canon CanoScan 8400F Flatbed Scanner that has max 3200 dpi with 48 bit colors. you can see full specifications for this one
here