This is the wet, braised style, not the dark KL version, so the calorie count is lower than people expect. A 442g plate has about 200g of noodles, which is 260 calories, then one egg at 75, four prawns at 50, and some squid and pork belly at 70. The stall fries it in lard and finishes it with a spoon of sambal, and that is the last 80. Total around 522, which is under a plate of char kway teow at 742.
The size jump is the real issue. The S$5 plate is the 522 calorie one. The S$8 plate at the popular stalls is not a little bigger, it is about 50 percent bigger, and it comes with more prawns, more lard and an extra egg. That plate is closer to 780 calories. Two people sharing a S$10 plate get about 500 each, which is a sensible way to do it.
The sambal is small but not free. A full spoon of hawker sambal is around 40 calories because it is fried in oil. The lime is free and does more for the taste than the sambal does. Squeeze the lime, use half the sambal, and you have lost nothing you will notice.