I just finished my university studies while also working full time, but my situation is still quite different I think. I defended my CS PhD a couple weeks ago in the US where I also work full time as a software engineer. I had a math degree from my (non-US) home country, which was/is not properly recognized. (Should be M.S. equivalent, but there are arrogant and ignorant administrators in the US. Meanwhile my opinion (that I refrained to yell to them) is that the US B. S degree is equivalent to an above average high school diploma from my home country.) So for me it was important to get a US diploma.
Work and school took very long time for me and also for others I met in the same boat. I did it because I actually like doing research and plan to keep doing it. (My software engineering job is math oriented and it is full of interesting problems like compression, boolean optimization, graph partitioning, etc.)
Here is my take: getting a B.S. in CS may help you on paper, but I doubt it will matter much more than 5 years experience and you will not learn much new useful skills getting it. Getting an M.S will take a longer while, will help you much better on paper, but you should consider finances and family situation closely. Are you sure you need a CS degree? I have many coworkers with math or physics or engineering degrees. Any other direction you may consider? Like business and marketing? Augmented with knowledge of software engineering that may triple its value.
If you intend to stick to programming for life, I would also suggest (that you consider) getting involved in some open source projects (with your company's approval) that may look quite good on your resume and offset lack of formal training and may help with networking too.