A truly grand, effective strategy, I'd say.
If things start getting stale, mixing it up is certainly a good way to reignite the flame, so to speak. Her friends' cases are also rather simple yet effective ones. Cosplay sex and outdoor sex are great ways to change things up indeed.
As I understand it, it's not entirely uncommon for adult Japanese guys to find girls' high school uniforms attractive because of how they view their time in high school and the way that girls dressed during that time, not because they're necessarily interested in high school girls at their current age (though that certainly does happen too). So, it's on the list of cosplay outfits that quite a few Japanese guys would love to see their girl wear.