Welcome Gino!
I've just got into the whole buying/long term investing thing as well, and I can relate to your enthusiasm in just "starting out". I've bought quite a few sets over the past month or so and put them in the attic (dark and dry!). Looking forward to seeing some long term returns on them, eventually.
I do have 2 of the BTTF deLorean and 1 of the Ghostbusters ECTO-1. I've built one of each and have a deLorean for the attic, both great fun, especially the ECTO-1.
But...reading your post, it sounds like your kids would really love to build and play with them both. In your shoes (and assuming this can be done financially) I think I would let them build them; is it really worth the few bucks they will potentially make in a few years time, measured against the fun, enjoyment and interaction that you could get with your kids right NOW? Buy another one of each; stick them in the attic (the kits, not the kids! ;-) ).
I am sure the fun you will have enjoying your kids building the kits, watching the movies and interacting with them, will outdo any profit they will make over time.
Many members here may disagree, which is fair. But as others have said, Lego was built in the first place for playing with...I'd be tempted to just play!
My 2 cents anyway...
Gareth