It's generally accepted that shorter rest periods (:90-2:00) are best for building muscle size, while longer rest periods (4:00+) are better for building strength. Just like anything else in lifting, there are plenty of exceptions to this "rule". There are lots of powerlifters who use longer rest periods and build massive muscles, but there are also lots of powerlifters who use longer rest periods and never really develop as much muscle mass as they MIGHT with shorter rest periods.
If you are gaining weight but not progressing in your lifts, then give 3-4:00 rest periods a try. If that helps your strength grow then eventually that strength should be reflected with some solid muscle mass. It's one of those things where if you experiment a little you should find what works for you.
Personally, I hate resting. I usually change my weights then get right on with the next set. The exception to this is when I'm working into heavier sets.
Current PRs at 242, raw w/ wraps- 525, 355, 605, 1485
Roboro tui, perimo vester adversarius
(Build yourself, destroy your enemy)