Blaming bad candidates for losses isn't a one way street. Who were the Democratic candidates in the Attorney General and Secretary of State races? Were they bad candidates or not?
The Democratic candidate for Atty Gen was Stan Garnett, who was Boulder County District Attorney -- here's his Ballotpedia page:
http://ballotpedia.org/wiki/index.php/Stan_GarnettThe Democratic candidate for SecState was the incumbent Secretary of State Bernie Buescher, who had been appointed by unpopular incumbent Bill Ritter.
Googled 'bernie buescher gaffe' -- nothing. Googled 'stan garnett gaffe' -- he's a prominent supporter of marijuana legalization, but I can't imagine that'd be a big problem in Colorado. Both of them seem to be well-qualified, good candidates who were soundly defeated in a swing state in a year bad for their party.
You're right that bad candidates aren't a one-way street, but Democrats were the beneficiaries of bad Republican candidates in 2010 in Colorado, not the other way around.