I agree about the rust, which leads to me wondering why West coasts vehicles are generally cheaper than East coast vehicles of similar condition. Is it the simple fact that there are more to pick from becuase they don't salt?
As for size.... eh... I can agree when it comes to open spaces and forest roads but my uncles SJ410, I think pre Samurai, took some local tophies from bigger rigs and always seemed to get around the woods more easily then our Blazers and Broncos, the older bigger ones. With that said he off roaded competively so he knew what he was doing, and my uncles who didn't compete and just hunted, fished, worked in the woods all hade 1/2 ton sized rigs and for anything nasty a Massy, hey that kinda rhyms. I don't forsee needing anything small and specialized, if a 1/2 ton won't fit than I am hiking or biking. I think she is on me to buy a tacoma not so much due to the preception of better capability but because she is timid of driving a big SUV or Truck. With all that said, lol who do you think drove the 26' F350 moving truck for 6h when we moved? So not sure why she is timid now...
I see you are from Canada. I am under the impression that vehicles in Canada are about 20-30% more expensive than USA? That Tacoma still sounds very expensive, but many Japanese rigs over 20 years old are seeming to appreciate in value these days.
I don't know how the Canadian market is, but if you were looking at an expensive Tacoma in USA, I'd also suggest you have a look at the Frontier. You can get a very good truck for the money. Beat-up-old-and-rusty-Tacoma money can get you into a nice, well maintained, better condition and few years newer Frontier. Frontier can be had in 3 body styles, King Cab, Crew Cab short and Crew Cab long. I am not sure which of those 3 can be had with Pro-4x or Off-Road packages, but those offroad packages get you a locking rear diff. The Frontier uses the same running gear as a Titan and has a very good 4.0 V6 with a stout 5AT. The Tacoma has a nicer interior, though. Here's a great million-mile Frontier story:
https://www.motortrend.com/news/2007-nissan-frontier-1-million-miles-chicago/ MotorTrend jokes "how did it not rust away?" well, that was a Toyota problem, not Nissan.
Speaking of which, if that Tacoma is rusty, I wonder if Toyota will replace it's frame? I'd check that before considering it.
I think for overlanding, vehicle size doesn't affect much of where you can go IMO. I would choose vehicle size on what you want to have capacity for. If you want to travel lightly, get a smaller rig. If you want to bring the kitchen sink, get a bigger rig. Personally for me, I have a FS truck. I wouldn't be trying tight, technical trails in any truck or Jeep unless I had a crew with me that could help rescue. In regards to a tricky trail, if you are by yourself I don't think a smaller rig will be much better as anything so bad a FS can't handle, you may want to reconsider it in a smaller truck also.
Do you really want to fully articulate, lift a wheel, squeeze between trees, go bumper deep in mud with a RTT and 600 pounds of gear on board?
In the PNW there's a lot of trees and mud. I used to ride it on a DRZ400, none of it would be any fun in an overlanding rig, I kept my truck on trails that are or were roads, which means there was always enough room for the truck.