I'd wonder if taking longer shots/reducing rim attempts is in some way related to a need for him to be playing heavy minutes, with TJ Ford out. Looking at Game logs of minutes played, his minutes have gone from being quite low and managed with Ford healthy, to extensive minutes since(with basically 3 games of low minutes: Miami's 3 point explosion, The Dallas Bench game and the NJ game.)
It will be interesting to see what happens when Ford gets back, the ratio of rim shots could revert towards career norms, which would make Parker more efficient. Not sure if taking fewer shots at the rim is purely due to aging, or is partly a more precautious approach given the season and injury to backup. It's probably a factor, though I wouldn't say it's the only 1.