I'll add this in because I've seen a few others bring it up:
- Comfort is entirely subjective. I've driven the 4th and 5th gen back-to-back on numerous occasions. The 4th gen seats (cloth) feel very comfortable from the outset. The 5th gen seats (again cloth) feel a bit more stiff in the beginning, but you get used to them for long drives. I've also driven a few lexus vehicles. Neither the 4th or 5th gen feel nearly as comfortable as those, but we're getting into apples-to-oranges at that point. My reason for bringing this up is that I've never really noticed an extreme difference in comfort between the 2 versions.
- Everyday practicality. Bluetooth and backup camera (which come standard on the base trail, though not sure about the SR5) is definite a nice-to-have but certainly not necessary. Entune seems nice, but I'm not sure what it really offers over simply streaming Google Maps or Pandora from your iphone via bluetooth. Are any of these features worth the big premium you'll pay for a 5th gen over a 4th gen...again that's entirely subjective, but IMO no.
- MPG. 4th gen v6 and 5th gen v6 are very nearly the same with the minor difference of VVT for the 5th gen. The 4th gen is lighter, sits slightly lower, and I believe has slightly different gearing relative to the 5th gen. So if the 4th gen v6 has slightly better mpg than the 5th gen, I wouldn't be surprised, but the difference is likely marginal. With careful driving on long highway stretches and road trips, I've gotten 22mpg, sometimes 23 mpg, and ~19-20mpg with more mixed driving. Given how bulky and off-road oriented this 5th gen is, I'm perfectly okay with those kinds of numbers....everything is a compromise. I wouldn't let the marginal difference between the 2 v6's be the deciding factor for you...they'll be about the same in the long run, and obviously the 4th gen's optional v8 will be a bit worse.
In the end, they are both toyotas, both 4runners and they both work well. If all the subjective things like looks, comfort, practicality really mean a lot to you, then yeah the 5th gen is the way to go. If you just want something that will give you the best bang for your buck, especially if you are considering putting some mods into it, the 4th gen (either the v6 or v8) is without a doubt the better option. I love my 5th trail edition, but for the $, a mildly used 4th gen v8 (even with some suspension and armor mods) still comes in almost $10k below what you'd be paying for a slightly used 5th gen trail.