My router has been running just fine for a few years now but i noticed that the firmware is kind of old.  Should I update the firmware, for security reasons or for efficiency?  I have had my DIR-655 since 2009 and it has been chugging along great.  All the wireless connections work just fine on various wireless devices.  I also recently upgraded my internet service tier with Cox here in Phoenix and purchased a new ARRIS / Motorola SurfBoard SB6141 DOCSIS 3.0 Cable Modem.  And after getting the modem set up over the phone with a rep, my speeds have been amazing, whether its through the WAN port or straight from the modem to the computer.  
Sorry i got off topic.  Anyway, if anyone can give me some insight, I would appreciate it.  I read here in the forums that if it ain't broke, don't fix it.  I agree.  But I am a worry wart, and I want to make sure my router is not compromised in some fashion by running and old version of the firmware.
My router is the of course the DIR-655.  The hardware version is A4 (it says that on the admin page and on the bottom of the router).  The Firmware version is 1.21.  
On a side note, and I don't know if this is the norm or not, but when i am at the Tools Tab and Firmware, when i press the "check now" it says that this firmware is the latest version.  But, when i go to: http://www.dlink.com/us/en/support/product/dir-655-wireless-n-gigabit-router?revision=us_reva, there are clearly many newer versions.
Again, thank you all for your time and knowledge and I appreciate the help.