"We like to eat good food, drink beer or wine, take photographs, and hike/cycle(something active)... I'd love to know which towns and activities you'd suggest for the 3 days in the Rhine area..."
I'd pick Boppard for a base town and venture out from there. Boppard has a nice selectioin of eateries everywhere you turn:
Weinhaus Roemerburg - https://upload.wikimedia.org/wikipedia/commons/9/97/Boppard_Weinhaus_R%C3%B6merburg.JPG
Severus Stuben: http://media-cdn.tripadvisor.com/media/photo-s/02/e0/0b/ce/severus-stuben.jpg
Take the chairlift (or hike) to the Vierseenblick lookout where the river looks like 3 lakes; a series of trails gets you around the top of the hill - Gedeonseck terrace is just a few minutes walk from the lift:
Try the Klettersteig? http://www.damscheid.de/typo3temp/pics/3d5d833b9b.jpg
Boppard is well-positioned for outings. St. Goar's Rheinfels Castle is just to the south. Park in town and walk up for some exercise and views, or hike the trail south or north from the castle that skirts the cliffs for more great views. You'll find some rest stops at lookouts, like this one:
St. Goar's sister town to the south is Oberwesel - walk the old town wall there:
You can also walk up through the vineyards to the Guenderodehaus, the film set for a popular German TV series called Heimat, for a glass of wine and some outstanding views:
(Actually you can hike the cliffside trail between St. Goar and Oberwesel in about 2.5 hours and hit the G'haus en route. Great hike.)
From Boppard ferry across to the Filsen dock and drive north to Braubach for Marksburg Castle, the only never-destroyed medieval castle you can tour on the Rhine. It's great - and you'll get some cardio if you walk up here as well:
Enjoy Braubach's old town too:
From Boppard you can take an outing to some of the Mosel towns as well. Cochem and Winningen are lovely.