Scrub potatoes thoroughly with a brush; pat dry. Prick potatoes with a fork. Rub potatoes with the 1 tablespoon oil.
For a charcoal grill, arrange medium-hot coals around edge of grill. Test for medium heat above center of grill. Place potatoes on grill rack over center of grill. Cover and grill for 50 to 60 minutes or until potatoes are tender. (For a gas grill, preheat grill. Reduce heat to medium. Adjust for indirect cooking. Grill as above.)
Meanwhile, for vinaigrette, in a screw-top jar combine vinegar, the 1/3 cup oil, the sage, mustard, maple syrup, garlic, salt, and pepper. Cover and shake well. Set aside.
Remove potatoes from grill; cool slightly. Coarsely chop potatoes. Transfer potatoes to an extra-large bowl. Stir in spinach, bacon, eggs, and red onion. Drizzle with vinaigrette; toss gently to coat.