As with many of Oregon State Parks and especially those on the coast the best time is off season. They're all quite crowded in the summer, but empty in the "Discovery Season". Here's some pictures taken January, 2006.
Here we have the Scamp
Shipwreck. This is all that's left of the Peter Iredale. She was a 278 foot sailing ship. Ran aground October 25, 1906. This is all that's left. The first I time I saw her there was a lot there. We won't say how long ago that was.
The winter months can have a special attraction. The waves are often bigger and watching them crash against the south jetty is a treat. Just around the corner you can watch the cargo ships cross the Columbia bar as they head for Portland.
You can spend several days at Fort Stevens and still leave with things not done.