In my opinion you would really need to stir things up if you want the game to be worthy of the "book TWO" title, because beating the game once, and experimenting with a lot with different character builds, I had to realize that the game in its current form really lacks depth and polish in the gameplay and ruleset department.
I voted "party based" in both polls, but I think in your minds you have an overcomplicated image of a party based game, with individual character control, party AI with your team members following you around, different movement speeds, pathfinding, etc., and you're always thinking in terms of realism instead of gameplay and fun.
Although I know nothing about programming and game development, I think there are some simpler solutions for party based gameplay, you just have to look in another
direction. I know that most of you "old-schoolers" wouldn't even poke a japanese rpg with a stick, in a hazmat suit, but you don't have to like big eyed anime cuties and spiky haired 14 year old boy protagonists to appreciate the gameplay mechanics and technical solutions applied in oldschool, tile-based jrpg's. I've got most of these ideas from such jrpg's.
My first suggestion would be to have the whole party take up only 1 tile, making only the leader character, or the currently selected character visible. I think it would require no greater suspension of disbelief than imagining a party of 8 taking up a 1 tile space in a Wizardry game, and watching the game with the eyes of a single person in fps mode while there's actually 8 of you. This way the game could be played exactly like Book 1, you controlling 1 character on the screen (which is actually the whole party) in isometric view. This way you could retain, amongst other things, the tile based puzzles, and you don't have to worry about characters getting stuck on the other side of a door, or leaving them behind when a scripted sequence would start, etc. You would be able to cycle through your characters, making the mage the leader if you need high Lore skill to read some ancient text, selecting the Thief with the highest lockpicking skill when you want to open a lock, selecting the fighter with the highest strenght when you want to bash something, or move something heavy out of the way. But I'm getting lost in the details now.
But this way, combat mode should be separated from "peace" mode. The game already uses some nice "line of sight" system to determine if the monster can see you, but this time, instead of simply aggroing the monster, it would initiate combat mode (much like in the Fallout games), where you would be able to "deploy" your whole party in a square of 3x3 or 4x4 around the leader character, and then the battle would begin, making all of them visible and they could be controlled individually in a turn-based fashion. It does not necessarily have to be action-point based, no need to overcomplicate stuff.
There are a few other details I could add, but this is getting ridiculously long already, so I shut up.
I just wanted to mention a few alternatives how to keep the game simple, while adding some party-based depth to it. I wonder what you guys think about it.