Well if you automate it I can pretty much guarantee it will be spammy and useless. Moreover, the quality blogs recognize requests like that (we make fun of them on twitter)
When I guest post (or accept a guest post) it's *carefully* thought out as to relevance and quality. Whatever links are included are just as carefully thought out as to placement and anchor text. If it's not a solid win-win for both parties PLUS the users on the hosting site, it doesn't happen. Sure that's a lot slower, but I also never have link problems. Never.