I'd like to know what level your character is and what story act and chapter he/she is in. I'd say to go through the whole story at least once, and make another character to use your voucher on.
The recent quest change removed most side quests up to Moonwater. Silverfrost and up still has it's side quests mostly intact, though those later areas didn't have too many side quests to begin with. I'm currently running a KFM through the story and leveling process and she's right now doing the Gunwon city stuff. on a premium account (+30% to exp), I got level 55 (and the ability to do ultimate skills) by the time I entered the story version of Heaven mandate. Got level 60 somewhere around the "New Hong School" arc, and after feeding her a bunch of exp charms, she's now HM 6. I assume by the time I get to finish act 9 and are able to get talents and the temple of succession quest, she will be somewhere around HM 12, which would be the same as the voucher gives.
Since my account is currently running premium benefits, I can't calculate how the character would level without those benefits, but a full free character, I assume, wouldn't run that far behind. Anyway. Story is easy for the most part. The section I myself had trouble with was the Twisted Grimhorn area. It's a hassle to do it without the help of HM points or a better weapon, since the character is limited to being HM 0 and a story weapon with only two gem slots. other than that, story offers no challenge at all.
Oh, forgot this too. If they haven't changed it, I believe that if you make a new character using a voucher, you also get an outfit from the voucher's initial training area.