Whether or not it is worth buying a purebred or adopting a random bred cat from an animal shelter depends upon your attitude towards the “ownership” and possession of domestic cats. But putting aside for a moment personal preferences, I’ll try and look at it objectively to provide some guidelines.

Ethics
It is ethically better to adopt a rescue cat from an animal shelter than to purchase a purebred cat from a breeder. I don’t think I need to explain why but, briefly, I will. There are too many domestic cats in the world causing unwanted cats to be euthanised at animal centres. We don’t need to create more cats. Therefore when you adopt a rescue or relinquished cat you potentially save a life; the life of an unwanted cat who might otherwise have been euthanised. This is a very rewarding aspect of this form of acquiring a domestic cat.
Price
When you adopt a rescue cat you pay a adoption fee which is considerably less than the price that you will pay to purchase a purebred cat from a breeder. Fancy purebred cats can cost anything from $500-$20,000. Purebred cats aren’t worth it in terms of value for money because what you are buying (compared to a rescue cat) is a more refined appearance at least potentially. So the purchase price is satisfying your desire to own something which looks nice or superior to a rescue cat. Although this is not always the case. There are many beautiful random bred cats at least as good looking as purebred cats. And there are many poorly bred purebred cats.
Longevity
In order to achieve the refined look of purebred cats you have to inbreed them to fix the genes which create that beautiful appearance. Inbreeding can reduce the lifespan of a domestic cat. It is my belief that purebred cats have a lifespan which is something of the order of 20% less than random bred cats. I am generalising. Some purebred cats will live longer than random bred cats and vice versa but overall what I’ve stated is, I believe, correct, which leads me to health.
Health
You might find that your purebred cat has an underlying health problem connected to the breeding of the cat i.e. inbreeding. For example, Persian cats have breathing problems and a high percentage of them suffer from polycystic kidney disease (PKD). Their coats are overly long so you need to groom them to help the cat maintain her coat. They suffer from to tear duct overflow due to their flat faces. The Persian is a particularly bad example of health problems in my view but even the magnificent Maine Coon can have hip dysplasia i.e. joint problems and other health issues which are “built into” the breeding process. When you inbreed and fix the genes for appearance it seems you also fix the genes for inherited health problems. In random bred cats you don’t get this sort of problem. That is not to say that you don’t get health problems in random bred cats. You do, but they are unfortunate rather than created deliberately.
Attitude
If your attitude towards being a cat guardian is about being closely bonded to a domestic cat who you love and whose appearance is second to the cat’s character and your relationship with them then you will probably prefer not to purchase a purebred cat. If your attitude lends itself towards cat “ownership” and the possession of a beautiful creature who you can show off your friends and which improves your status in the community then you will tend to purchase a purebred cat and deal with the negative consequences as mentioned above.
Refining the rescue cat adoption process
You can refine the ethical benefits by adopting a blind cat, a three legged cat or a cat with any other disability. That’s even better and even more rewarding. It is a great start to the relationship to adopt a cat who really needs your support.
Are purebred cats worth it?
For me they are not, but the money isn’t an issue for me. The ethical issues are the ones which drive me to adopting rescue cats. That is not to say that I do not admire and like the thought of living with a beautiful purebred cat. I would like it and I do love the appearance of these magnificent pedigree cats. However, the ethics override this desire.