DHH actually did follow Spolsky for 7 years and only after running out of ideas and constantly hitting brick walls they started investigating a rewrite to rejuvenate the product based on new ideas that weren't around when they first built it. I guess, the answer is, rebuild only if you can't build your new ideas anymore and you can't attract new customers. (He calls it becoming japan in the talk.)
DHH actually did follow Spolsky for 7 years and only after running out of ideas and constantly hitting brick walls they started investigating a rewrite to rejuvenate the product based on new ideas that weren't around when they first built it. I guess, the answer is, rebuild only if you can't build your new ideas anymore and you can't attract new customers. (He calls it becoming japan in the talk.)