I have 8 acres in the center of our place that was clearcut in the 90s when my dad was alive. He didn't want to spend the money to replant and since it was surrounded by pines it grew back in very dense loblolly. Around 2010 I took a small dozer and cut lanes through it, then took a chainsaw and thinned it further, then started it on the burn rotation. It was 20 years old before I did the first thinning, and the only reason I was able to get it thinned was that I had a crew in to cut other places. Now that 8 acres looks about the same as the rest of it, without the cost of planting.
As far as the future quality of the timber, there was a time when the mill at Thorsby didn't want sawlogs from planted timber, only from natural stands. I'm not sure that's still the case, but slower growing timber makes better lumber, so I don't think that will be a problem for you. Planted stuff will grow faster and should theoretically bring more income, but would it make enough extra to justify the $400 in planting cost? I doubt it, and it's sure to get harder to even get 40 acres cut at all. And with 3 sons you have a lot of future free labor to carry out the thinnings.
I would go this route if it were me.
The only reason I wouldn't is if I could get NRCS funding to replant in longleaf. That's your tax dollars they are giving away; might as well get some if you can.
