I've lived in Venice, smack dab next to Marina del Rey, for over five years now, and I've only recently discovered Burton W. Chace Park, a quiet swathe of greenery tucked into the marina. If you want a maritime atmosphere without braving winds, waters and/or nausea, then rest your tush on one of the grassy knolls here and gaze upon the seafarers moored in the yacht parking lot.
There are lots of BBQ grills and picnic tables, and a couple dog runs. Other that that, you've got benches and grass and that's about it. A really cool thing I've learned about, however, is that the park offers free bird-watching tours. The two-hour guided tours for adults are scheduled once a month on Thursdays. See the park's website for more.
Families: If you've got tots in tow, this is a good place to let 'em run out some energy. I brought my toddler here yesterday afternoon, and she had a blast chasing pigeons and sea gulls. But she's always ready for a good playground, which this place lacks, so afterward, we drove southwest for about 5 minutes to Playa Vista Sports Park. (This is maybe not the most politically correct destination for some, given the Playa Vista development's controversial history, but wow, what a great playground. The library nearby is fantastic for little kids too.)
Penny-pinchers: Come during the week, as the on-site parking lot requires quarters for its meters on weekends and holidays only.