This is very fundamental. You see; where, in my opinion, retail went wrong is that they think they made the game 'challenging' where it actually is painfully annoying grinding. If you could find a balance in having the challenge of leveling up and gathering items, instead of being it a bore, you can have a very successful server.
I think if you involve party experience and, as you said, adjustments to the vitality system, it can help to achieve that (like if all party members have Vitality level 4, it gets an additional boost etc.). Perhaps you can also adjust small things to it like; boosting the experience you get from overhit kills (you usually get an exp bonus from that, so increase that bonus a bit) good players that can time their skills well get easier level up that way.
Just my few 'hints', perhaps I come up with more later. Good luck with the server! I bet it'll be great :)