Full-time 4x4 gives you traction all the time and you get a combined mpg of 25, that is amazing. I actually am a car moder (that means I modify my cars so they aren't stock). I suggest that if you want to change anything about this car it would be; get Yokohama AT/S tires for the best all around traction no matter the surface and the tires will last you forever, get performance intakes and filters to help with higher rpm performance. Those are very basic, if you are looking for anything better I suggest you go to RAV4world.
Versatility, Reliability, Excellent mpg for a 4x4
The 2.4L engine is a large improvement for the 2004-5, plus you can add a supercharger or turbocharger if you want more power for that engine.