If becoming a robot to be able to walk is an obvious no brainer, shouldn't normal, able bodied people fall over themselves to become robots to get xray vision, or whatever the special ability du jour is? Becoming an alien to get an arm is ok, but do it to get a tail and it's no longer a sure thing?
Ultimately fiction tends to turn against such notions pretty hard, indicating it's nore about normality than functionality.
To conduct a proper cost-benefit analysis you need to evaluate risk as well as reward, and think over the range of alternatives rather than just a binary "do this Y/N?"
To give an example I'm near-sighted. Wearing glasses is both reversible and imposes little or no risk as a treatment, and brings quality of life nearly on par with normal sighted people. Getting lasik could possibly improve my quality of life, but is also irreversible, even when successful it involves thinning the cornea, and the possibility of a screw-up on their or my end is very real. In a world where glasses didn't exist, were very costly, or had their own risks, my calculus on lasik would be different though.
The same underlies the theoretical scenario of getting a bionic eye that is better than a regular eye. Would a bionic eye bring an improvement in quality of life? Perhaps. However you also have the many risks of having your eyes surgically removed and replaced by binoics, such as it needing replacement, it being rejected by or damaging the body, it going off warranty, it getting hacked, all of which are risks that'd be nonexistent if you'd stuck to existing.
I'm very pro-transhumanism, but I feel like in terms of order of preference things like bionic eyes might well be near the bottom:
1: Doesn't require surgery. (ie glasses)
2: Requires minor surgery (cochlear implants, I guess you could argue that a cyberpunk USB jack on people would fall here then anything attached into A)
3: Requires major surgery (pacemaker)
4: Outright replace body parts (binoic eye)
It'd also definitely be below A here and arguably below B depending on the specifics:
A: Grow replacement body parts. (still requires surgery, but replacements should be as good as original, and solves the reversibility issue)
B: Brain in a jar set-up that remotes into other machines or bodies. (radical, but eliminates a lot of risks for organic or cyborg bodies)
You also have cases where there is clear benefit but accommodations are normally adequate. For example humans and other primates cannot synthesize vitamin C in their liver like most animals, which puts them to being vulnerable to scurvy. Genetically engineering humans to do so would've been very useful to the sailors of yore, but in modern civilization not being able to have vitamin C in one's diet is rather rare.