@1
Classical and rapid are for progress, blitz and rapid are for fun.
How effective would blitz chess be for me?

@1
Classical and rapid are for progress, blitz and rapid are for fun.
Does blitz not help at all?
@3
No blitz does not help.
The main reason is that blitz is not worth to analyse, while improvement comes from analysing your lost games.
The only benefit of blitz and bullet is that it gives you more confidence in time scrambles: that you can play at a pace of 1 move per second if needed.

You've been playing here for 6 1/2 years, 4300 games, and a 1600 rating? Not a beginner.
You should be playing blitz as well as rapid, and my recommendation is 3/0. Anybody who says blitz doesn't help is just wrong. Even for beginners, it helps, just not as much as playing (and going over) rapid games.
Since you aren't a premium member right now, I would recommend that you spend some time on Lichess doing their puzzles, as well. All these things help your game in different ways.
I have researched a lot and have found many mixed answers, the general consensus is that blitz chess is pretty harmful for beginners, and that you should play longer time controls. I have generally been playing rapid and have gotten to 1600, but I wonder if at this point playing blitz could be useful as well or is that only for 2000+ rated players?