> it's very easy to come up with something that looks really good but is horribly broken in subtle ways that you won't find until it's too late.

My experience has been that this doesn't matter in a lot of cases. A product can be both, highly useful and subtly broken.

One of the biggest boons to my productivity was realizing when something is good enough and to move on. You can waste so much time tuning for precision and recall.