Specifically in reference to not being able to get good colonies started without doing loads of exploration, one thing I find particularly helpful in that area is to take notes on any interesting survey or exploration missions that come up, even if I don't end up accepting them.
For example, if a mission to scan a mining station in a remote system pops up, I'll just throw "Mining station, trappist system, asteroid field" into note pad, and once enough of those notes have come up, I head out already knowing where a lot of the high value stuff is. The same can be done with planets. If a mission to survey a Terran world shows up, bam, instant knowledge of a habitable world, with no resources expended. Just mark it down, and check it out when it's convenient to do so. The majority of habitable planets make workable, if not necessarily excellent, colonies, so its a good place to start.
Further, if you run shepherds or throw survey equipment on some of your logistics ships, you can get most surveys down to only 5 supplies, which makes it easy to survey all the random planets you fly past as you do other activities. With the cost that low, you tend to make a pretty substantial net profit on each survey, even if you aren't really scoping out for colonization.
Another handy thing to do is to throw down some com relays in various outlying systems. They don't cost anything to maintain, and will give you new bounties while you are already out of the core worlds, and so they are sometimes very easy to reach, saving fuel and time.