How valuable is being in an A+ rank CS conference with a short paper? My paper is accepted in an A-rank conference in computer science as a short paper. I need to reduce it to 6-pages instead of 10-pages.
All the reviewers said the paper has all the required elements to be a decent paper, but the presentation and problem introduction should have been better. 

Also if i have to cut 4 pages, I need to reduce the references and the propositions and the proofs, and some of the related works!

So I'm not sure if it is better to withdraw it from this conference and submit the revised full version to another one? Or i should take the opportunity of having my paper in this top conference and try to submit the extended version to a journal paper?

BTW, i'm almost at the end of my PhD study and have not yet published any paper in a top-tier conference, and this work is one of the main results of my work (however there might be one another work to be submitted to another A-rank conference).
I'm wondering how valuable is to have a short paper in a top conference?!


That depends a bit on what you define as "valuable". As Buffy says, having a presentation and presence at a top conference is certainly very valuable in terms of visibility in the community and opportunity to make connections (never underestimate the importance of those!).

However, in my experience, as a line in your CV, everything that's not a full paper counts for very little, even if it's a short paper at a top conference. In other words, if that is intended to be the main paper of your PhD and you intend to go onto the job market with this work, you need to get it accepted as a full paper. If it's just a side project, or just one in a longer string of papers that together form your PhD, leaving it as a short paper and taking the opportunity to attend the conference and get your name out there may be worth it.

I should also say that, assuming your reviewers are right and all it needs for this work to become excellent is some presentation-level cleanup, it feels like a pity to not do this small additional work and try again at the next deadline for a top venue, rather than downgrading it to a short paper.