I focused heavily on tactics for a few months and my blitz rating jumped from 2000-2250 in that time. I've never really played blindfold chess, but practicing solving chess tactics will force you to visualize the board a few moves in advance.
How much rating did you improved by playing blindfold chess and solving puzzles?
I've tried some blindfold games against my computer... it always seems like a reasonable idea, but then after a few days I'm reminded why I quit last time... it's unrealistic (99% of the time) to need to visualize that many moves ahead. In a real game you get to use the board as a reference, and rarely will you need to see more than 5 or 6 moves ahead.
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Solving puzzles (not speed puzzles) greatly improved my visualization though. I don't know how many rating points, because I was doing other things at the time too (like playing games and reading chess books). But a few hours a day for a month and I noticed a big improvement in my calculation (and I could see the final positions easily).

My Online rating here stagnated around 1350 for a while. I spent... maybe a month and a half seriously focusing on tactics (and even then, not for very long per day), and my rating climbed to 1500. I then went back to not really taking things seriously.
There's a definite correlation between meteoric improvement and tactics problems.
I want to know how much did you improved and how much your rating raised.