I've had good luck with it in terms of indexing, it really does help with getting new posts out there quickly. Although that also depends on how fast those companies update as well, so pinging posts out at the same time usually does the trick.

In terms of ranking it's decent for some initial links to posts, but each site is different - give it a shot with a few and see where it goes from there.

I'm trying to use RSS submission but still can't get it right. I have a problem with converting URl's into RSS feeds.

whatever you do, it's about getting seen so yes, submitting your posts to rss directories is another way to promote your site.
nothing wrong about that
beside that i highly recommend to transfer it into different pieces, e.g. reports, podcasts, slideshows, etc. we all prefer to consume content differently and that is, in my opinion, something people oversee:
e.g. i don't have time to read tons of blogs but it would be super valuable to have a post from a blog in a podcast and listen to it while doing laundry, clean the kitchen or workout
sorry, a bit more than you wanted to know but hopefully it helps

Just learn more from you Guys, sharing tips