The desirable .org domains that sell tend to fit the niches of the typical non-profit company, i.e. terms related to charity, education, religion, conservation, fund raising etc. There are many dictionary word .orgs that are unregistered because they don't fit these niches. The only obvious exceptions to this rule are huge search volume dictionary word business domains like mortgage.org , games.org, etc. which have sold for big bucks AND some 3 letter LLL.org domains.
I have a few dictionary word non-business .orgs that I have been sitting on for years and never received a single offer. In contrast, I sold a 2 word nature related .org for low $x,xxx .
So in general I'd say MOST .orgs have reg fee value if they are not in the groups mentioned above and because of the very low sales volume (only 100 .org domain sales are recorded by namebio for the last 2 weeks versus hundreds PER DAY for dotcoms) it will take a long time to sell.
Here's some recent .org sales over $1k that illustrate what sells:
tdi.org 2,555 USD 2015-08-23 NameJet
csocollegecenter.org 1,426 USD 2015-08-22 GoDaddy
americanwoman.org 1,500 USD 2015-08-21 BuyDomains
e-islam.org 1,001 USD 2015-08-19
Flippa
thehealingpath.org 1,566 USD 2015-08-18 BuyDomains
e-islam.org 1,001 USD 2015-08-19
Flippa
06.org 11,144 USD 2015-08-13 Sedo
drivingtest.org 3,700 USD 2015-08-12 GoDaddy
pod.org 2,200 USD 2015-08-11 NameJet