The penalties for not eating/drinking/sleeping, and also radiation poisoning, were not noticeable enough. I played through the whole game on hardcoe mode and I'll be honest, it really had no effect on me. I ate, drank and slept just to get rid of the labels telling me I was hungry, thirsty, or tired. I never did so because I felt like I was suffering.
I completely agree regarding the vanilla version of hardcoe mode - it didn't work for me because food and drink were too plentiful and you only needed to sleep about once per week.
After installing Harder hardcoe Rates (Refined Rates) and Expensive Wasteland (5x prices) mods, then food and drink became more scarce and I began suffering sleep deprivation effects more frequently.
I'm confused about your post however, you said that you didn't eat, drink or sleep and you never experienced any penalties. If you go long enough without doing this, even in the vanilla version, you die. That is a pretty serious penalty.
If you continue like this for a while, before dying, your stats are reduced as follows:
DEHYDRATION: -2 PER, -3 END, -2 AGL, -1 INT
STARVATION: -3 STR, -2 PER, -2 CHR
SLEEP DEPRIVATION: -2 INT, -2 END, -3 AGL
As a result of installing the mods, I spent most of the game suffering from some of these effects, as well as hobbling around with all my limbs crippled, and I died from dehydration several times. Whether it is "realistic" or "immersive" etc., doesn't matter to me, but I found these challenges made the game much more fun to play.
I could never go back to playing without a modded version of hardcoe mode. In fact, I went back and installed some mods for Oblivion that do the same thing. (COBL Real Hunger, Real Thirst, Real Sleep Extended), and I very much hope Skyrim implements some kind of survival or hardcoe mode similar to FNV.