I wouldn't overextend if it isn't financial feasible to make a purchase - you could only replace one and alternate upgrade years/releases which is a strategy
@rui no onna has discussed before. These prices on these are a serious consideration. What do you do on your iPads? Is there one where you consume content more or create artistic items on more? That would be the one to benefit from OLED.
That said, I do find the discourse around the display somewhat amusing. The iPad ostensibly exists
for the display; it's a display you hold in your hands. So any time there is an improvement to the display it elevates the entire iPad experience - this was very true of the transition to Retina, less so the movement to 120hz and mini-LED. All that to say, I think a screen alone can be enough of a reason depending on the person.
Personally, I'm moving from a 12.9" iPad Pro M1 to an 11" iPad Pro. I wanted to consolidate my larger iPad Pro and iPad mini, but I would have been willing to upgrade 11" to 11". Depending on configuration you'll be getting more RAM, faster CPU/GPU (depending on your needs), a new battery, and a MUCH improved display on the 11" and considerably improved on the 12.9" (I found the blooming and off-axis viewing on the miniLED quite disappointing).
I am cautiously optimistic about battery life. Apple stated that the M4 can deliver the same performance at 1/2 the power I believe. I'm hoping that for casual use the M4 will prove more efficient and that dark mode on OLED can make a meaningful improvement to battery life as I personally found the M1 battery life to be a disappointment.
If this is really the case and your current devices serve you well then leave it alone and think of how much nicer the
next versions will be in 2025/2026.