You don’t need 3 alts just to gain plots. Alts help sure in the beginning, as you can specialize and feats give you plots, but they are not required for plot gain.
At 10 plots per persistent pie, you could strip mine with bombs for decent xp and reasonable coin.
You could run a hunter on a teaching pie for reasonable coin and decent xp.
Line up a whole load of machines pop a teaching pie for your crafter (log him out) and get decent xp when they finish.
That’s how I do it anyway. Caving was okay but doesn’t really match bomb enhanced strip mining (large blast radius bombs give you xp for all the stone) I’d still call hunting meteor spawns more effective if you get a decent run but not by a lot. The crafting route of course has an infinite amount based only on how many machines you have and rock (or raw materials) to put in the refineries/crafting tables.
I now at 300 hours can generate 150k xp while my crafter is offline, but this is only going to keep scaling up and up and up. - That’s offline, sure it takes a time to line it all up however. I can do one level 10 plots a pie on my strip miner and about the same (a bit more) for the hunter on teaching pies. If I could afford to strip mine with teaching pies, well LOL.
What I am saying is. Plots nah. Not an issue. Certainly newbie alts and accounts don’t gain the rate my experienced characters do. I have a hundred free plots sitting on my miner, and this is with me taking plenty of free space for various landmark projects I want to do already. Its having friends and a busy shop or portal network that brings in footfall.
I’ve just put in for an account upgrade, because i like space, but it doesn’t bring me any more money in. The advantage is however I can border off land, which you need to do now to stop your beacons getting split up when they get too close to a settlement. So instead I am using boundary beacons, or will be when I get upgrade to keep the integrity of the main beacon cluster intact.