We reuse, but we also have quite a few different kinds of ornaments, so we could conceivably do a silver and blue tree one year, red and gold the next, and all-vintage the next, all without buying anything more than we already have. We did silver and blue with the additional weird one-off ornaments the last few years, but this year we switched to all vintage plus one-offs, and I really like it. The red and gold ornaments have literally never left their boxes, I should donate them(and the eleventeen strings of incandescent lights we no longer need since the tree is prelit) so someone else can have festive decor.
We did have to make a purchase this year, though. The front of our house has no outlets, so we bought 6 strands of solar lights last year and put two on each of the vaguely cone-shaped trees that flank our walkway, plus a strand on each section of our decorative fence. Had to buy two more this year because the trees grew and needed more lights. We could have gotten by with one, but the lights are a weird blink pattern(3 options vs either 2 or 8 on everything else I found), so I wanted to have a backup.