I've done a few liveaboards and have summarized below but in short, you are paying for better boats (more modern/updated, better finishing), more privacy (that may mean more square feet per person on board), ensuite bathrooms and private rooms, AC, 24 hour power, better food, plated instead of buffet, and definitely a higher crew to passenger ratio. (I recently had a 16 passenger to 13 crew ratio.) On some itineraries, don't just pay attention to the price as you say but look at the number of dives that you also get. You sometimes go from no DM to having a DM or even better, a better DM to diver ratio or more experienced ones when you pay more. I haul along camera gear so having camera friendly areas, dedicated equipment for care and maintenance is also something that I only find on a nicer liveaboard. The list goes on and on....but hopefully that gives you a gist.
Here's what I've been on:
-California's version of Blackbeard's out to the Channel Islands (Truth Aquatics - bunks, if you could even call them that, and 2 showers shared, 1 changing room, and a couple of bathrooms shared). informal dining, no table service, not enough seating for everyone to eat inside or all sit at once. 3 meals a day. no dive guides or DM included. you're on your own for getting your gear on/off and in and out of the water. They just fill the tanks and run the boat. Bare bones. nowhere to charge gear if you're a photographer. nitrox was an option.
-Mastro Aldo (Komodo Dive Center) for Komodo - private rooms and bathrooms but the bathrooms were not necessarily en-suite..but they were yours and only yours. AC. 4 meals a day plus snacks. plated dining. 1 DM for every 4 divers. diving off dinghies, assistance with gear (assembly, don/doffing), etc. room cleaning service daily. beer and wine not included. personal service. no power between certain hours at night. no nitrox.
-Raja Ampat Aggressor and Spirit of Freedom - private rooms, ensuite bathrooms with AC. dailyi room cleaning and turndown service. 4 meals a day plus snacks, beer and wine included on the Aggressor but not Spirit. 1 DM for 4-6 divers depending on group and skill level of divers. diving off dinghies, assistance with gear (assembly, don, doffing, and cleaning/rinsing and drying at end of trip), extremely personal service, MUCH larger boats and nicer finishes, power 24 hours a day. dedicated camera area/room with lots of power options. nitrox an option. pre-and-post trip arrangements like transfers to hotel or airports, etc.