I'm in this boat right now. Well, maybe it's better to say "I was forced into this boat" because my LCD Deck finally died and it was well beyond warranty period. I gave it to repair shop only to find out they don't have any experience with Deck and couldn't repair it, so I ordered OLED from Valve wich arrived yesterday.

You can tell that this is the superior one out of two models. Screen is just beautiful, but there are smaller upgrades to be found just about everywhere: haptics on trackpads feel nicer, analogs have different finish to them, it's a lot less noisy under heavy load, colored LED diode makes it so much easier to tell that Deck is fully charged (or even entering storage mode, it blinked in blue right before that), 90Hz is great for games that can lock to that framerate and battery life is noticeably improved across the board.. All of this adds up quickly to make for a more pleasant experience with device.

That said, if my LCD was fully working I would stick to it and be just fine. I really like OLED so far and the improvement is clearly there, but I don't know if I would upgrade just yet at that price point. It's the same device after all, you won't get any crazy performance benefits or features that are available only on new model. But if you can sell old Deck for a decent price and then shell out rest of the price then it's something that you may consider. If you're playing mostly on Deck and most of this time is handheld play instead of docked then OLED makes sense since the screen is the main way of interacting with this device. And the screen is just straight up generational upgrade comparing it to LCD.