So I'm currently a lvl 30 slayer, and I'm considering getting a 7 day xp boost with gold in game.

Is it worth the gold investment, or should I just save it for when I hit 60?
If I did get it, would it be better to follow the quests or just grind on mobs?

It's worth it only if you know what you are going to do.

If you follow the leveling guide below, you will get from 30-60 in less than 7 days guaranteed.

30-31 Sinestral Manor runs.
32-37 Desert fire mobs.
38-39 Cultist's Refuge runs.
40-41 The "Core" quest line.
42-54 Dragoon mobs.
55-60 Moguta's or Grizzlies.

Alright thanks.

I take it I should catch up on the story quests after grinding out each zone?

Yes, the storyquests lead you to each of these zones. If you're overleveled for them, just do the orange ones and skip the yellow ones until it brings you to an appropriate place to level.
Also, I probably wouldn't do instances if you have the 100% XP boost running, since questing/grinding would likely be faster in most circumstances

This post was edited by MetaSheep on Jun 19 2013 01:10pm

Agreed instances take quite some time if you are a dps class, Tanks(lancers) que quick.

42-54 dragoon mobs you must be crazy. WAY too low to start grinding there at that level, good place to level though

Any recommendations then? I'm lvl 40 at the moment.

if you quest smart, questing is the way to go.

I did all the quests up to about 50 then started to do the orange ones to 60 worked efficient enough for me.

Got my slayer, berserker, and sorceror all through that.

42-50 in about a day.

This post was edited by Cattotonic on Jun 20 2013 01:12pm