I would say if the LJ is paid for keep it and buy a dd for work or going out of town. I traded my tj for a 2012 4 door rubicon. I love it. Benefits by far are the lockers, 4-1 x case, smooth ride on road and suoer capable off road. Im planning 35's with mine and a 4.5 in to help with some clearance around my neck of the woods. My buddy just bought a 2012 sport, his plans 2.5 in RK with 35's cut fenders, 4.88 regear with rear locker. He is building his for more of trail rig vs mine is my dd. I bought mine in october last year and had valve noise. Had bead replaced twice because i had the first one done too early and they pulled an original off the shelf. Im hopeful for this one though. No loses in power. Great motor. I have 33's currently. Getting 15mpg.
That being said, make a list of the upgrades you would do and figure out what it would cost. And also lust out pros and cons. I wouldnt worry about engine issues. And the 5 speed auto is awesome.
Capability wrapped in AWESOMENESS!!!