Don't edit spam posts. There are almost no exceptions to that rule - even for truly obscene posts, a flag is much more effective, and much less time consuming, than editing, and will destroy the post quicker.
In general, you shouldn't edit spam posts because, as mentioned in the answers to Magisch's post, it makes moderation more difficult - the spam becomes less apparent, people don't flag it as readily, and it ends up taking more work from more users to clean up properly. There's also the chance of invalidating valid flags, if the post is rolled back, which would reset the spam-deletion counter to zero and require even more work.
It also, as mentioned, messes with spam detection heuristics - while Stack Exchange's native spam blocking system doesn't currently do anything with the bodies of posts (it works with IP addresses), there are a few community run spam detection systems, such as Smoke Detector, which rely almost totally on post bodies. Editing links to be unclickable would result in one post being scanned twice, with different results. Again, that results in more confusion, and more moderation work to clean up.