If you already have a good DI AR and just want to buy the "Bentley" of AR's go for the LWRC SPR. With the same amount of money, you could also spring for a Noveske or even Knights Armaments which would represent the "Ferrari" and "Lamborghini" of AR rifles. They are DI guns, however.
The LWRC will most likely outlast you unless you shoot over 2-5k rounds every year in carbine classes. With that said, things that will most likely fail is the piston spring. After that, parts known to break is the piston rod and of course your normal bolt wear / breakage. The SPR's are really nice and even the most staunch piston haters have to admit that the SPR is a fine rifle. It's one of the lighter piston rifles out there and the quality components are second to none. You do pay for that quality, however. Just keep in mind that if anything breaks, there's really nothing you can do with it. You have to ship it back to LWRC for repairs. There aren't any local gunsmiths who will know what to do with the thing.
The BCM Jack carbine has the bonus of being all milspec, so you can swap and replace any part. Any gunsmith familiar with AR's will be able to fix or troubleshoot anything that's wrong with the weapon. I'm a huge BCM fan, but for the price of the Jack Carbine, you could just spring for a Noveske or even a KAC if you don't mind some proprietary parts since you are considering an LWRC. If this is your 1 and only rifle or your "go to" rifle, then I would probably stick with DI or spend an extra $500 buying a bunch of spare parts for your LWRC.
Good point. Getting both would definitely be the best case scenario.