Should I resubmit a modified computer science conference paper to a journal? Here is the situation; I made an article that got published in a Computer Science conference; the final decision was that it was considered a borderline paper. After a while I got an email from the organizers of that conference, letting the authors know that there would be the chance to resubmit our articles to a journal, but that the work should contain at least 30% more contribution than the original paper. Long story short, I worked through all the reviewers comments and added more information on my original article.

Actually I am a little bit afraid if my article would make it through the journal, but because I worked hard on doing the asked changes I would not like to leave it like that.

For that reason, I was wondering that in case of a rejection, Could I submit my expanded work to another conference; or should I just leave it like that? I am afraid that maybe the reviewers from another conference could see it like a case of self-plagiarized, even though I am citing my original article. 

What to do in this situation? Should I paraphrase all the article again before submitting it with the new material? or should just let it be?
When in doubt talk to your adviser. 

It is common in the Computer Science that the delta between conference and journal papers is 30%. That is not updated text only, but 30% of new substantial material, such as new experiments etc.

When submitting paper to a conference, there isn't a 30% rule. Your new paper needs to have a stand-alone novel contribution. 

The reason is that CS adopted an iterative publication style workshop -> conference -> journal. So if your extended paper does not get accepted to a journal, you can attempt another journal, but not another conference.