If all you want to do is run DS roms then that setup will be fine and you do not need to run flashme upon your DS.
Flashme is able to get rid of the health and safety screen, it helps guard against Trojan code (they are around but as far as I know nobody has even been hit at all in the last 6 months), reduces battery drain (albeit not really noticeably) versus your nopass, allows execution of certain wifi based homebrew and can make life easier for stuff like DS card save readers.
The only real downside to flashme is you void the warranty and some patchers it seems cause their patched roms and download play to have issues.