Remember, with the Wrangler, it comes in two flavors...short wheelbase and long wheelbase. The LWB version can carry TONS of stuff! In fact, it probably rivals that of the 4runner in terms of cargo hold!! Go see for yourself! The LWB can easily hold 4 people...rear legroom is around 35 or so. Sure, it is not as comfortable as the 4runner...but the Wrangler is not advertised as a cross-country SUV, even tho some use it as such. It is primarily an off-roader that is streetable. Think Porsche GT3 or something like that...a racecar that is streetable. The good thing is that the Wrangler is more affordable than GT3!
The SWB, my favorite, is for the more hardcore off-roaders who want clearances and compactness in an off-roader/weekend car. The LWB is for those with other priorities in life.
As for mileage, lets use EPA since it is something that we can compare across the board scientifically. The current Wrangler EPA is no worst than the 4runner. It weighs almost as much as the 4runner too because of its thick frame and solid axles. It has poor aerodynamics because it is such a classic design AND the design itself serves a purpose off-road. Until this year, you could not get a decent automatic tranny.
Now, do you need 35" tires to make it capable? Hell no. A stock Wrangler Rubicon (LWB or SWB) will run circles around a Hummer H2/3!! In fact, there was a video of a Rubicon driving BACKWARDS up a hill while the H2 was scrambling for traction (going forward of course)! A stock Rubicon will molest any stock 4runner off-road...even if the 4runner has proper tires. IMO, a stock Rubicon is the MOST capable stock production vehicle on the planet, bar none (including Defender). (Unimog etc. don't count.) Remind me, is the Hummer still in production? Is the Wrangler still? Despite the flaws, the Wrangler is still selling well.
Rubicon buys you: Dana 44 hybrid axles, super strong lockers (top even among aftermarket stuff), 4:1 transfer case, 32" BFG MT tires, sway bar disco's, etc.. I am sure that i am forgetting something but you get the picture.
So, isn't it nice to have THIS much off-road capability AND still get 21 mpg on the highway with regular gas?? I think so. It just depends on your point of view. If you're used to a grocery getter, then yeah, the Rubicon makes no sense. But, if you're into off-roading, then the Rubicon can be very delicious...dare i say efficient!!
But yeah, like ANY vehicle, if you modify it OUTSIDE factory specs, then expect to get penalized for it. If you put 35" tires on any SUV, then your mileage will suck, esp. if you don't fix the gearing! (I am pretty sure your cross-country friend didn't adjust the gearing etc. for his 8 mpg Jeep!)
Lets talk about reliability. Sure, it is no Toyota, but it ain't a typical Chrysler either. Jeep Wrangler has always had half decent reliability. But, since it is so popular, it can also be fix at numerous independent shops...and the parts of it are relatively cheap. What sets the Wrangler from any other Jeep products is its RESALE VALUE. I would bet that it rivals (or even beat) that of the 4runner! You won't have trouble selling it at a decent price.
Call me a fanboy if you want to...but, yeah, i like Wranglers!