Honestly if you are looking to just hit the mountains and do some fire roads and back road trails there are tons of vehicles that will do just fine. I have a 89 YJ 4 cyl and it is perfect for my uses. I use it when it snows to get to work and I get out into the mountains anywhere I really have ever wanted to go. With that said I have no illusions of taking it on Rubicon or slick rock, it would die in a ball of fire. But I get 20 + MPG everywhere, and yes it will do 75 mph on the highway, just takes her a bit to build up steam.

I have three other vehicles so adding a fourth that I was only going to use occasionally meant that I was more concerned about long term cost than performance. But even with some pretty rough trails in allens park and some in the adobe desert on the western slope my little 4 banger has done everything I wanted and more. I did not want a trailer toy, I wanted something that I could drive to the trails, have fun, and get home reliably and my jeep does that wonderfully. I have 31 x 10.5 tires on it and very few "upgrades" meaning that I have around $3000 total into it. Also the insurance is cheap compared to my Tacoma that I used to have.

You can throw a bunch of money at anything to get a sweet rig. I saw the most bad ass early 80's subaru brat at the sand dunes, it had a supercharged 350 and 36" paddle tires on it. The most capable off road vehicle that I have ever seen was an old Suzuki Samurai, the wheel base is so short, they are so narrow and if the gearing is right, they are so light that they just crawl up anything. But if you are just looking for a moderately cheap way to get out into the mountains, a stock jeep will do just fine. Lifts, giant tires and engine upgrades are a waste on 99% of jeeps because their owners never take them anywhere that a stock jeep could not handle. Knowing how to drive off road safely is big too, and I have seen many people bust the hell out of their rigs taking them through relatively easy trails.