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.)
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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.)