The attractiveness issue seems like a moot point if individual users are choosing what to allow (unless you're suggesting that the spammers would eat up so much bandwidth that the site would cease to function properly). I mean if you're talking about individual aesthetics, I can make my journal plenty unattractive without the help of spammers if I'm so inclined. I don't know why I'd do that, though.

Similarly, if I thought spammers were making my journal unattractive to my readers, I would select options that allowed me more control over content, maybe even screening non-DW users. Or (heck), only allowing comments from OpenID folk that I have on my Access List.

As for the using up resources issue, if that's really a consideration, I'd think that would be solved by making it only an option for paid accounts.