We have moderators and (eventually) 10k users who are more than happy to keep the less-than-ethical folks at bay. I don't see that as being an issue.
I also see absolutely nothing wrong with making a recommendation where its appropriate. Its your discretion if you make a link or not, however. For instance:
Try foo.com, they really excel at this
sort of thing
Is much different than
or just http://foo.com
If it 'feels' spammy, don't make a link. If not, make a link. Still, there's nothing wrong with promoting something you found useful in good faith. High rep users and moderators can take care of the rest, just like we've done on SO. The first thing I usually check when using the 10k tools on SO are flags and the list of activity by new users, for just that reason.
Self promotion is another matter, and it really depends on the context of the question and your reply. Again, discretion is paramount, we'll let you know if you zigged instead of zagged :)
I found nothing wrong with the question in question, if that makes sense :)