Re: BRASS BLOCK HELP!
1) Yes, they are noticeable. Whether or not it is an improvement is up to your ears. I have noticed a difference in sustain with every block I have installed.
2) I can't speak to whether it will make things too boomy, but what I have noticed with brass blocks is less that they warm things up, but more that they muffle some harsh resonances. I don't think you'll notice too much low end coming in -- it's more a case of addition by subtraction.
3) The only way to know is to measure -- either you'll have to measure, or hope that someone else has.
4) It does inhibit things slightly, but you'll likely already have the strings slack and sticking to the pickup magnets or have the trem bottoming out on the recess in the top before it becomes an issue.