The effects of meditation are best compared to those of sleep. A good night's sleep doesn't make up for lousy sleeping habits the rest of the week. But getting enough sleep _regularly_ is key to being healthy, happy, and productive.
Ditto meditation. Trying it once in a while is likely as waste of time. But practicing it regularly (and getting better at it, which you will, with practice) can have positive effects, over time.
As an aside - Zen takes a good deal of commitment, but it's the least 'bullshity' of all the approaches to meditation/mindfulness I've encountered. Eight Gates of Zen is a great intro: http://www.mro.org/zmm/training/eightgates.php