Further improving PhD thesis vs publishing as a post-doc I am a PhD student in mechanical engineering in The Netherlands, with four months left on the 4-year contract, writing my thesis. I have sufficient content to be able to submit the thesis by the end of the contract, as far as my supervisor and I are concerned. It is going to be a collection of papers that are either under review or have been published.

Although it seems the thesis can pass, I am not entirely happy with the whole as a body of work. For various reasons, I have obtained results relatively late in the process. I feel that a proper reflection and utilisation of these results would require 4 - 6 additional months, in order for me to be able to process and write it down. 

Though there is funding, my university is generally not willing to extend PhD contracts. It would likely be possible, though, after submitting my thesis, to continue as a post-doc and work on publishing said results.

Up to this point, I have felt inclined to work on delivering a very good thesis, and considered working on it without pay for those additional months. Upon reflection, it seems that this is largely due to my emotional investment in the PhD project.

Is there any reason career-wise (I am still debating an industry or academia career) that it is better to work on my PhD thesis than to take the post-doc position and publish the papers after the thesis?
(Obviously, financially, the post-doc option is highly preferable.)
You can always revise and extend your old work. Make your dissertation work as good as you can in the available time and then move on. If the problems you work on are sufficiently interesting there is always room to continue. 

Whether you continue the work with your advisor or not may be a question that depends on the expectations of your field. 

Most doctoral students hopefully finish with a notebook full of problems that were interesting but couldn't be completed during the graduate program. The ideas don't die just because you graduate.