My NT has increased blocking from about 25 to about 35 over the last 2-3 seasons and he's become a much more dominant force over that time, but whether thats to do with blocking or increasing other attributes (mainly vision/confidence/speed rather than agility/strength, which have only gone up slightly in that time), or due to VAs for D-line being pretty good (Heavyweight 4tw!). It can't help if you've got a few SPs lying about, especially when you're getting to the high levels where you already have all your key stats capped to their varying levels.
Wouldn't recommend triple capping blocking though!!

Any increase in blocking might easily be worth 7 points in a season. On helping someone else take an INT/fumble back for a TD!