The 512 LCD Deck is a stupidly good deal at 25% off... $330 USD is crazy cheap for a new Deck, and that's a solid amount of starting storage space before you even move to grab an SD card.
I own both in the household, and while I do enjoy some of the OLED Deck's improved features, the original is NOT a slouch... I wouldn't sleep on it! The display is MUCH better than it was at launch thanks to software fixes, and the screen can safely be overclocked from the base 60 Hz up to to 70 Hz with minimal effort, further reducing the gap between the models (OLED is 90 Hz) and allowing clean locking to 35 FPS, a great balance point for smoothness vs battery use.
Since I own both, I can tell you what you'd mainly be missing taking the LCD: basically you'd giving up battery length (OLED is about 25% better on battery life... but the whole issue is mute if you primarily play older games, or mostly play while plugged in), about a half inch of diagonal screen real estate, plus you're taking a somewhat less precise touch screen, and taking a slightly older Bluetooth adapter in the unit. In exchange for this, you get a new Deck for more than $200 less than the base OLED will cost.
Otherwise, these two are very similar, so it's a very good time to get a Deck.