Boomkin healing is usually more of an emergency thing. For example when you lose your healer, a boomkin can help keep people alive for a short period of time so you can down the boss.
Some variety of dreamstate/resto build is a viable spec for leveling (is there anything that isn't?) that allows you to heal instances and solo fairly effectively. I leveled as a DS/resto until 73, when I started to find it more difficult to heal Northrend instances without Wild Growth. Doing things like healing or tanking in a DPS tree works fine at lower levels, but really starts to get hard in Northrend. Not that you have to have a full resto spec, but it makes it possible to do the instances with just about any group, rather than just the decent ones.
Anyway, if you intend to heal at end-game, now would probably be a good time to go full resto anyway, and get your practice in. Hitting 80 in a full set of blues from NR normal instances makes it easier to jump into heriocs.
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That monster in the mirror, he just might be you. -Grover