It's literally hundreds of dollars more per night for light snacks and drinks.
I think it's debatable on the "light" part. When we were there, they served quesadillas, chicken skewers, potstickers, quiches, coconut shrimp, etc. It was enough to make a full meal most of the time. It's a bit lighter during the lunch/midday time, but they still served a crudité platter and chips/salsa/hummus. Plus, you can get unlimited sparking wine, beer, and soft drinks. For us, I'm not just paying for the food/drinks, I'm also paying for the increased dedicated service (CL CMs, turndown service). It's more of a total package, which I think is fairly decent at the $250-300 extra per night price.
When you think about how many CMs are dedicated to just CL guests, the cost would need to be much higher to pay for a wage that would be what they get now + tips that the few guests that do give them to balance out. When we were there in December, there were 3-4 CMs on the floor restocking, cleaning, organizing, chatting with guests, another set of CMs comes in for the later shift. That was on top of the two concierge CMs. So, a total of maybe 10 CMs per day (lowballing it) dedicated to just CL guests. Now, you have to add in the cost of food that is brought in, the drinks that are available in the fridge, the liquor in the back. And all of that for an average of 3-4 people per room. I would consider the cost to be pretty good for what is being offered.