SERP#1 - What do I do now?

I've been reading posts (mostly Google) here for the past year and used the advice to "optimize" my site, www.woodenpropeller.com. It's an informational, non-commercial site without any real keyword competition. Now it's been in the #1 position on Google and most other search engines for the past 6 months or so for kw's "wooden propeller" or "wooden propellers" and quite a few other more unique kw's. Once I got to a PR5 and about 60 backlinks, nothing much else changed.

I feel like I should be doing something more pro-active, and at the same time I'm reluctant to change anything for fear of triggering an adverse action from Google. In reading some of the "Sandbox" theory discussions, I get the impression that longevity has its own benefit (maybe with or without new efforts to optimize).

Any takers?

If it's non-commercial and #1 I'd say you are done besides maintenance and occasional link building.

If it is commercial, I'd say working on conversions would be priority #1.

I wouldn't recommend change anything you have now, instead, you can try to expend your SEO efforts by working on related content keywords.