Is the risk of my nose looking worse worth it getting better?

Almost always, the main risk, given a good pre-op evaluation, is that you could get less improvement than you were hoping for, not that the nose would get worse.In evaluating a nose for revision, I list everything we'd like to change, and evaluate how predictable those features are to change, and try to let the patient know the most likely outcome.From these photos, you seem to have some features that are on the more predictable side to improve. Your nose is strong in its forward projection from your face. The tip can be brought back closer to your face. We call that "de-projecting" the tip. Making a nose smaller in some dimensions helps in revision rhinoplasty, because then, any remaining problems rest on a smaller, less prominent nose, so they are smaller themselves, and tend to bug us less.Your two tip cartilages seem to be strong, which means that modifying those cartilages can bring the tip closer to the face, and also narrow the tip a bit and make the curves of those cartilages at the tip less noticeable.On the profile view, it seems that your bridge is strong up at the top of the nose -- in front of your eyes, or just below your eyebrows. When the nose is strong there, if the tip and bridge are de-projected (brought closer to the face), it's important to reduce the strength of the bridge up there at the top, or your profile would resemble the profile of a Roman statue, where the profile of the forehead slides right down onto the nose, without that little dip we like to see in front of the eyes. Search for Roman statue profile to see what I mean. Your surgeon must pay attention to that, too.Finally, although your chin isn't a *problem, placing the smallest size chin implant can draw attention away from the nose, without adding any unwanted attention to the chin. 
How *much* to narrow the tip, or deproject the nose, or lower the upper part of the bridge? We figure that out with morphs, well before surgery. I'd love for you to see some excellent professionally-designed morphs of what could possibly be done with your nose. Morphs could also help you identify what's bothering you, and help you set a goal for the rhinoplasty that's accurate for your tastes.  (Side note: in my opinion, morphs should always be done by the surgeon, or he should direct an assistant as she makes the morphs. Morphs should be made with a constant eye to what actually *can* be done in surgery, for that particular nose, and only the surgeon has that information and judgment. Another aside: I also recommend that you not show morphs made by one surgeon to a different surgeon. If a surgeon makes his *own* morphs, you get to see whether he understands the important issues of your nose, and how your nose should be changed. But if you show the surgeon someone else's morphs, and he says "Of course I can make your nose look like that," then you don't really know if he fully understands, or even recognizes, the important changes shown in those morphs. And you don't know if he can make those changes during surgery.)
Remember that rhinoplasty is an exquisitely difficult operation to get right, and you should only have surgery if you are able to make yourself very confident in your surgeon's skills. The changes that your nose needs require advanced techniques, and skill that most plastic surgeons don't possess with expertise. For most noses, it's much better to not have surgery than to have inexpertly-performed surgery. Read my essay on how to stay out of trouble while selecting a rhinoplasty surgeon. And for those who have had previous surgery, it also discusses how to tell whether your first surgeon should be performing your revision. And it also discusses how to take photos that are best for online evaluations.
Your nose is also a perfect example of why computer imaging is mandatory in rhinoplasty. You need to know exactly what the surgeon is planning to accomplish -- what features he thinks he can change, and by how much he thinks he can change them. I always email morphs to my online rhinoplasty consultations. When you see the surgeon's goals in the morphs, you'll know whether he has an eye for an attractive nose, and whether he shares your opinion of what constitutes an attractive nose. You'll also know whether the changes he proposes are large enough to be meaningful to you, and whether he understands your wishes enough to address all of your priorities. How would you ever get that figured out without the morphs?

This is the standard question in revision rhinoplasty. There is always the risk that a nose will look worse than what you started with in revision rhinoplasty. That is why you have to limit your risks.This is done by having a consult with a surgeon that regularly performs revision rhinoplasty. Then you and the surgeon have to set conservative goals that both of you can agree on. Still at the end of the day, one of the options you have to have is to be able to accept what you have and not proceed with any surgery.

Rhinoplasty carries risks whether it is the first intervention o subsequent ones. If you can determine accurately what you would define as a 9/10 rather than leave it to the surgeon's  evaluation your chances increase. In technical terms, it seems that you had a cephalic trim with little change in the contour of the domes, and spreader grafts to make the shape more continuous. This leads to an even contour of the bridge and tip. These points can be addressed, and if your goal is a nose that has a slimmer look, it is definitely possible. When the columella overhang is reduced and the nostril lowered, many patient feel the tip looks wider. A computer simulation would help you to decide how much change would be required for you to feel you are achieving your goals. Everybody has different likes and dislikes and accurate planning would be very valuable for your decision whether to go ahead or not. 

you have been given good advice by the previous surgeons... I would simply add that my take is that you are a bit too short/over-rotated, irregular in the dorsum and your tip lacks refinement/defining points are too wide... hence, if your version of a 9/10 is to refine your dorsum/tip and add a bit of length/de-rotate you then it is realisticAs far as risk goes, you have to do your diligence to minimize it... i understand that there isn’t much transparency in this business so visit a few qualified revision rhinoplasty experts... start with surgeons (both plastic surgeons and ENT facial plastic surgeons can fit the bill) who have been in practice a long while; have a practice focused on rhinoplasty; and who do difficult revisions... don’t fall for a computer imaging ‘con-job,’ rather be sure that the surgeon can explain (with or without imaging) exactly what’s planned and simply see how much confidence you develop Good luck

Unfortunately, the more the nose is operated on, the less predictable the scar tissue can heal. The risk can be higher than the reward if you go into surgery for the 4th operation. I would recommend seeking a board certified plastic surgeon or facial plastic surgeon that specializes in revision rhinoplasty and weigh the pros and cons. Best of luck to you!