Get a Jeep Wrangler. Though the engine is highly computer controlled and "hands off", you can have a lot of fun bolting everything you can imagine onto the Jeep itself.

I added a pop-top roof, solar panels, dual batteries, a water tank,pump and filtration system, interior cabinets, a fridge, new suspension, bumpers, a winch and a whole lot more to mine!

All the details here: http://theroadchoseme.com/the-jeep

I designed and built the whole thing, which was channeling my inner engineer!

Some cars (like the Miata) are still specifically meant to remain more or less tinkerer-friendly, but yes, unfortunately the trend seems to be doing everything possible to force you to visit the stealership for even the most basic of repairs (headlight bulb replacement, oil change, etc.).

I would pay a healthy premium for a solid off-road-capable vehicle that wasn't intentionally as locked down as possible. I imagine one of the chief challenges is manufacturer fear of NHTSA or EPA retribution when someone releases an ECU image that turns a Prius into a rolling coal in exchange for a bit more power. I doubt this is going to change without explicit regulation protecting tinkering.

Volvo tried that with a concept car designed to meet "the particular needs of female drivers": https://en.wikipedia.org/wiki/Volvo_YCC

And it is funny because that's the case of basically everything, yet at the same time, being a maker is fashionable and for a reasonable amount of money, people can and do get themselves 70's industrial level workshop in a lot of what was trade only fields.

Can you be a little more specific? I find modern cars to be funnier just because of the closed source stuff. It's more rewarding (for me, at least) when i figure out a can bus message or how to flash my ECU with diy adapters.