I don't think there's a right answer to this one. You can try different things, but I'd advise you to be diligent in their degree of success, moderating their application as necessary. What you implement as a reward for those capable of or interested in "deeper" roleplaying may very well turn out to be a punishment for those who aren't.
I do, however, submit the following tale.
About two years ago, I moved. My old group had, with a few variations, been gaming together for about thirteen years. Back then, when I was only reluctantly considering finally making the switch to 2nd Edition, my games had a lot of the elements that were common from the games I played in the 80s... they were very combat-oriented with fairly two-ply characters. (At least I had finally put my Monty Haul tendencies behind me.)
Then, in late '92, a new gamer in town dropped into my group and, without ever realizing what he was doing, managed to completely transform my group's play style. He had only played D&D for a few short years, but his previous group had been extremely character-oriented, where the players focused on roleplaying and character development like they were a group of playwrights. And this was how he played D&D. And I had a front-row seat to one of the most fascinating phenomena I have ever had the joy to witness.
It was inspiring. By carelessly treating his PC as an actual person, with individual motives and agendas and a full range of human emotions, he injected my group with a type of frenzy to explore this alternative approach to characterization. I was actually caught entirely off guard when the players started eating up huge swaths of game time with in-character discussions, roleplaying with NPCs, and an investment in setting up dramatic scenes. I wasted no time feeding this movement, bringing NPCs to life with a new depth and exploring the players' emotional investment in their characters. I spent the next several years learning how my players responded to various stimuli, establishing a level of drama appropriate to each individual interest.
Now don't get me wrong... some players jumped headlong into method-acting, others didn't. I still had a powergamer and a strategist in the group, and one guy who was more interested in his character's cool powers than his personality, but they all tuned in to the games potential for character development because it gave them the opportunity to be individuals in a powerfully group-oriented construct. The other players may or may not be interested in how kick-ass you are, but they were always interested in what your character
thought about the situation, or how she felt, etcetera, etcetera...
But two years ago, in the wake of my divorce and pursuit of a new romance, I moved to a new town and quickly collected a new group of gamers. They were old-school, gaming with another group on a different night that (unknown to me at the time) was generally a very hack-and-slash type of unit. Without really knowing what I was getting into, I got things rolling in the manner I always did. I constructed adventure material that was packed with exciting combat challenges but also explored the individual characters' responses to dramatic elements couched in the midst of the adventure. I was trying to get to know both the players and their characters, without realizing that they weren't even in the habit of getting to know their own characters.
If I'd been as cocky as I'd gotten with my old group, this would have been very risky. But I never assumed that anything I offered would be precisely what they wanted, so I mined them for feedback, watched their reactions, and took their cues when constructed further adventure material. And they responded very well... but not to the degree my original group had.
I think one of the main reasons that my prior group had been so malleable, so easily inspired, was because we were younger. We were college kids. And anyone who's reached their 30s can pretty much corroborate that we are a lot less prone to radical change of our core persona than we were when we were younger. And that includes what we look for in our primary entertainments. As gamers, we are a product of our experiences. We can still adjust to new ideas, particularly if they represent a possibility we've never previously encountered, but we're always going to be most comfortable with the things we've enjoyed all along. Most of us are no longer looking for an innovative gaming experience. We know what we like about our D&D game.
And of course it's important to recognize that there is
nothing wrong with hack-and-slash, powergaming, wargaming, a focus on your character's cool new powers, a fondness for problem-solving... nothing wrong with
any of that in your D&D. If it's not what
I want out of my game, as the DM, then it behooves me to inject the elements that most interest me. So my NPCs are dynamic and loaded with personality, my campaigns include character-driven plot elements... and my hack-and-slashers are slowly turning into roleplayers.
Life is good.
Sorry for the long-windedness. I hope this can provide some inspiration, or at least a ray of hope for those in similarly difficult circumstances.
