I concur, keep the 12 valve.

I bought a 2001 24 valve manual 6 speed quad cab 4x2 in 2016 with 97K on it for 15,000, it tows my Race Dakota and lives in my garage, 103K on it now, absolutely love everything about it. It's show room perfect, what I really like is it's exactly like my late fathers truck, only his was a 12 valve and I didn't buy it when he passed, I've tried to since, no luck.
Fast forward to a couple months ago, I bought a 2007 one owner 4x4 24 valve with 125K on it for 15,500, it's as clean as the 2001, but...It's gonna be a money pit, 68rfe, VGT turbo this and that, DPF this and that....$$$. I bought the 07 replace my 2500 98 5.9 gas RAM work truck, but I'm selling the 07, keeping the 98, I love everything about the 07 except for the future repair bills, and they are gonna happen, get on the Cummins forums.
I should have done my homework.