Someone mentioned that 4Runners are exspensive to maintain.
That has not been my experience at all. My 'Runner is a '97 4x4, all it has had is regular maintainence, nothing has ever failed.
It is the most reliable vehicle I've ever owned, and I've owned quite a few.
I have owned a Nissan truck, and will never own one again.
Having worked as a mechanic in the past, I got to see how different makes of cars were made.
No one beats Toyota for all-around build quality, and reliability.
As for that Altima, like all Nissans, they depreciate faster than Toyota's (as has already been said).
In 5 years, your 'Runner might be worth around 18,000. That altima might be worth 8,000.
There is a reason for that.
I have considered getting a new 4Runner, but my old '97 (which still looks new) drives just as nice as the day I bought it.
And it's size makes it more manageable on 4WD trails, plus the new ones don't have the rear E-locker.
If I were you, I would find a way to keep the vehicle you have.