Switching from Feral to Resto or BoomkinFollow

IMHO druids should ALWAYS be stashing off-spec gear in the bank. I'm as feral as they come but whenever there's no clear upgrade to my feral gear as a quest reward I'll take the best possible casting piece. Then the next time I'm in town I compare new with old and keep whatever's best. Every once in a while I respec balance or resto for a change of pace, and now that I'm in a real guild I can offer up to respec (temporarily!) as needed.

As far as your leveling quandary it really depends on your goals. You should know that questing is generally acknowledged to be the best experience/hour and fastest way to level. So if 80 ASAP is your goal I'd recommending sticking with what you know and are geared for, quest away and drop in on dungeon runs for fun when you feel like it. Tanks are usually nearly as in demand as healers, and as feral the ability to DPS or tank should make it so you have NO problem getting into instance groups as you level. Then if you want to heal at 80 respec in your mid to high 70s to get comfortable with the spells and tricks of the healing trade.

If you have your eye on 80 but are itching to try the change-of-pace of leveling as caster DPS for a while, just respec balance and give it a go. Might want to spend a few levels in your current spec collecting decent gear, but leveling/questing is pretty much a faceroll so you should be successful enough even if you just grab a bunch of +spelldamage and int gear on the AH.

If you plan on being an end-game healer and want to level via instance runs in that spec all the way up so you're completely comfortable as resto, despite the fact that it'll slow down your leveling pretty dramatically, go for it, but understand your non-instance questing/grinding will be veeerrry slow. While you're leveling you can get away with healing instances as balance for sure and even feral.

Before you keep leveling, it is definitely worthwhile leveling your mining & herbing so you can herb/mine in the area you are questing in. Being able to sell the extra resources you get while questing will make a massive difference to your bank balance for almost no extra time (other than the time spent catching them up to your current level). Having said that, depending on your servers economy, the lower level mining & herbing mats might actually get you enough for your level 60 mount before you even start continuing to level.

For the record, I agree with this so universally that it was with great hesitation that I recommended buying caster gear with a little intellect and spell damage if OP wants to try out balance. Two times I've played around with balance specs, and both times I was underwhelmed by the experience, and that was WITH a decent off-spec set I'd been collecting. Trying to play moonkin with no intellect or spell damage at all wouldn't be very much fun.

While mining and herbing are some of the highest gold-makers, there is a very annoying drawback: you constantly have to shift from detecting mining-nodes to detecting herbing-nodes and back. A more convenient combination of money-makers would be mining/skinning or herbalism/skinning. But that is just a preference that sprouts from laziness.

Regarding to the low levels: like Friar says, up those skills and you will see your gold skyrocket. Always keep your gathering skills up to or even above the level of nodes that are in your current questing areas. And these days there is a huge plus to the moneymaking from gathering: the pre-Burning Crusade ores/herbs/leathers are selling for huge gold these days because there are loads of level 70-80 players that are picking up the crafting skills that need those mats.

(for example, on my server, rugged leather sells for 55-75 gold per stack of 20; thorium ore for 75-90 gold per stack of 20)