You don't say if there is any particular point in the CIPS ethics code that you cannot agree with. If there isn't, go forth and sign it. If all that bothers you is that your ethics (as manifested by competency) will be assessed by someone else who sees things differently, and that this will somehow make you "unethical", in my mind it is not an issue.
Allow me to elaborate. First, background disclosure, to help you decide whether to ignore the rest. I have some advanced degrees and I've taught at universities in addition to my day industry jobs. I am very comfortable with calculus among other fields. I code quite a bit when required (and it usually is), and I rather loathe Java. I tend to do lots of IT and DevOps stuff in addition to my real job simply because there is no one else around (e.g., in the startup I am with now) who can do it as well as I do, but I am not a provider of IT services as you are. I may agree or disagree with what you write on occasion, but do carry on - I will be awaiting your future columns (Drew - good call...).
I generally avoid being a member of organizations or societies, but I have been in the past, and I carefully checked the by-laws and ethical codes every time. Some companies I worked for (the really big ones) have ethical codes, professional conduct codes, etc. I had to sign those, too. I always made a point studying them. I must say I was quite impressed by both the apparent intent and the specific formulations and I never thought, "I shouldn't really sign this, but I will, to stay employed."
1. To answer your main question: Being a member of a professional organization will not really make you any different, nor will it make you a better or worse techie than you are. It does not define you. It may be a (perfectly ethical) tool in making your sales pitch more attractive to prospective clients, but it will not mean that you'll do your job any differently. It will be up to you to add to the professional society's credit - consider it an incentive.
2. Subscribing to an ethical code does not mean you cannot make any professional mistake from that moment on. I've never seen an ethics code that says, "making mistakes is unethical." If you "forget" to point out to a customer that designing a wirelessly controlled pacemaker or insulin pump with insufficient security (or pre-installing a certificate hijacker on a laptop, for that matter) will expose the end user to real danger just because you are afraid the contract will go to someone else, then it's a question of ethics. Generally speaking, it is about recognizing a conflict of interest. Is there anything that you would have done differently if circumstances were different? If at any point you recognize that something should not be done and do it anyway - that is when your ethics should be questioned. Offering your services while recognizing you cannot do the job is included - the term "competency" seems related.
3. By all means get a degree if you feel it'll be beneficial, either as a sales pitch aid or as a step to personal fulfilment or - hopefully - both. A degree will not, by itself, change you. Nor will it make you a better techie in any narrow, specific sense. A (good) university is not a vocational school, its job is not to add a specific set of skills to your repertoire. It may make you a better, more methodical learner and it may help you approach completely new problems with no known solutions more effectively (especially if we are talking about a master's degree). Again, it will be up to you to add to the university's reputation.
4. Most importantly to remember in moments of self-doubt: you are not, repeat NOT responsible for any expectations others may have of you. You cannot be. This includes your technology skills, your writing skills, everything. This includes the simpletons who think that if you have a university diploma or some membership card you will provide a better service. This includes any expectations that someone may have that you will never, ever, screw up. Your personal or professional ethics does not mean infallibility.
Best of luck.