Should I quit my PhD?

If it is impossible to compile a thesis from all your publications, I suggest focusing on lesser publications in the thesis and if it is possible to expand your work, focusing only in one direction. Since your work is already published, there is no reason why it wouldn't be accepted by the reviewers. The content of the thesis counts less in applying to post-doctoral jobs, what is important is your papers. Of course, the thesis must be well written, rigorously, etc. There are many people who receive PhD diploma with few publications, or even no publications at all.

I really have to disagree with everyone here telling you "don't quit" as though it would somehow be a failure, and a Ph.D. is the thing to have, etc. I would say:

1. It depends on why you've gotten to this state of affairs

Having invested time and effort in 5 different and barely-related directions over 5 years means something is seriously wrong. Probably not wrong with your capabilities though - since you have been able to obtain useful novel results. There's some kind of issue with one or more of the following:

• Your motivation: How come you haven't chosen to pursue any of these subjects further and more deeply.
• The relation with your advisor: How come your advisor was essentially completely uninvolved in those papers? Do you even have any sort of interaction with him?
• Your advisor's motivation: How come your advisor did not want you, or you and him together, to focus any any of the 5 subjects? Or on another one? Hasn't he solicited you, advised you or told you to do certain work that he would be familiar with?
• The research proposal / plan which you presented your candidacy with: Did you originally decide to just jot something down you don't really care about or your advisor doesn't know about? If so, why was it accepted? If not, why didn't you sticking to the plan? Or - after 2 or 3 years, why didn't you sit down and devise a new plan?
• Potential collaborators: Why are you working alone? It seems the community, or several ones, are interested in your work enough to have it in conferences. So, have you found nobody else to work with? Have you looked?

I can really not give you a serious answer without some or most of this information. But I will say that for some of the possible answers to this question, you should definitely consider:

• Taking an official leave from your Ph.D., to figure out what you want or would be passionate about.
• Adding a co-advisor, or even switching advisors, to someone who would be able to help you finish by focusing on a subject you've already started work in.
• Quitting amicably, if there isn't clear direction or subject you want to focus on and get more results, and if what you'd really like to do is go work in industry somewhere.

2. That's not the right question

Getting a Ph.D. is a side-effect of performing a body of significant research on a focused subject. Do you want to do that, still, and (do you believe you) are capable of doing it? ... Answer this question, in light of what I've said above, and your own question resolves itself. Again, I can't venture an answer, since you've not provided enough information.

No don’t quit, five A* papers is more than most theses ever achieve already, good work!

Sounds like you just need to come up with a vaguely convincing story to knit them all together; then find some friendly examiners. There must be some bizarre application area that would combine most topics somehow... say you have published on category theory, the social science of Hadoop uptake, and tractor design; then you just need to invent some niche application about farmers needing a more robust language and system to handle their agricultural data, write 20 pages of waffle about it as an intro chapter, staple that on the front of the papers, and you should be good to go.