(REAL MONEY CONVERTED INTO GAME MONEY = NEP )
AFAIK, you can only use NEP in factors of 10.
So regardless you'll always have some left over, it's a BS gambling tactic.
As for the value in game, at the moment it only saves you from grinding character levels(acquiring clothes) and buying characters.
But with each new character release, if you have insufficient NEP, you'll be granted just enough to purchase that character.
At least in Beta.
(if you spend it on something else, you're screwed atm afaik)
You ONLY get the 3 BASE characters for free: Alet, Erika, and Dr. Anya.
The others HAVE to be PURCHASED: Celia, Juzi, Elizabeth Carter. +New characters yet to be announced
(Galatea apparently has been approved, with a height modification and no release date yet)
I would assume eventually you will be able to purchase other things with NEP, probably everything.
So to answer your question, barely any value ATM.
And there is zero confirmation that any NEP gained or any progress you've made on your account during Beta will be saved and not wiped clean with the official release. Remember this is an ONLINE ONLY game, if their records are incorrect you'll have to contact customer support.
Which is AFAIK non-existent, or through Discord. Unless you're banned.
And even then, the second this game is abandoned you're paid content is smoke in the wind.
"YOU WILL OWN NOTHING, AND YOU WILL BE HAPPY" -SomeAsshole