"Could you not also just remove the pages that are getting bad quality links or rename them? That would also discard your valid links as well but if that page is getting a ton of poor quality links I would think its the content that is attracting them or a bad off page campaign. If you dont 301 the old page and you just leave it as a 404 eventually those links would be discounted in Google or removed by the webmaster whos linking to you I would think."