World of Warcraft → Level as one spec but transition to another as I near 100?

So I've been leveling my druid as guardian. It's great, she is beefy and not afraid of elites. I like to continue doing that as I go 90-100.

I'm not planning to raid tank though, will probably play as boomkin in LFRs...

So has anyone else leveled as one spec but transitioned to another, but keeping both, as you neared 100?

I was thinking I'll hit up as many treasures as I can to build both sets, maybe with some crafted gear, but queue LFR with boomkin as my spec. Or if the tank gear is better, queue as kitty but have my loot spec as boomkin...

I always level tank/something (love dual spec) so there is no problem for you to have both specs while leveling up. You can practice your balance spec while solo and use guardian when you have to do group quests/elites.

Don't worry about getting gear for your off-spec, use the follower missions. My most recent 100 had a full bank tab worth of tokens for gear. Most of them have at least a 20 slot bag worth when they hit 100. I park all of my alts at the garrison and run missions three times a day, morning, afternoon, and evening focusing on gear (both toon and follower), gold, and resources.

I wouldn't worry about switching until you ding 100. Game play always changes at max level, so what you did while you leveled changes once you're at max.

One thing I'd recommend doing is once you are in Nagrand, change your loot spec before turning in quests that award neck, ring, trinket, or weapon/OH slots so that you can get the INT once you want. The other slots will have AGI/INT so no big deal there. It will make transitioning from AGI to INT for proving grounds and dungeons much quicker and less expensive.

These are all very good suggestions, thank you!

How high do you want to gear up and how quickly?