Hoople - 4:23 pm on Jul 6, 2011 (gmt 0)
Good point rainborick. Expanding on rainborick's thought:
Look at the pages these links com from. Those pages that have no/lesser value could always be set to return a 410 (status = gone) error rather than 404. This is a way to address your excessive 404 concern.
Personally I wouldn't throw away all of them, especially if they contributed to making your back-link profile look more natural. All sites have some marginally spammy back-links.