If you are not editing the image then yes you can leave it as a DNG. I don't think long term storage of camera raw proprietary formats is good idea.
A 5x7 at 360 ppi saves out as 13MB in 8 bits. Did you leave some layers and leave it in 16 bit for 85 MB?
If space is a problem aTiff with LZW compression can sometimes save a lot of space and is lossless.
Neil Snape photographer Paris printer reviews at http://www.neilsnape.com
|Hot Air Balloons Over Bagan by User9320321874|
|Blue mood by darub|
from Fixed lens shootout.
|Yellow Warbler by LeeS|
from A Big Year - birds
|Waiting for the Parade by tcoker1103|
from - La Vida Loca - (Black and White Street Photography+ A Border)