4 years (or even 1 year if you are super hard-core) of time is a pretty non-trivial investment. I was 2 classes away from a second degree and declined to take them, because the ~100 hours of work it would have taken wasn't worth the additional letters after my name. I also just really don't know anyone relevant who thinks that a college degree or lack thereof particularly matters (although the knowledge and skills acquired in the course of pursuing said degree may matter a lot). Good people will judge you by what you've done to demonstrate skill, not based on a college diploma.
I think IlyaShpitser's comment pretty much nails it.
I came to the same conclusion, and in general a lack of degree has not impacted me as I get employment based on demonstrated skill.
The main limitation is that any formal Postgrad study is impossible without a degree and this was a regret for me, prior to getting access to the coursera type courses.