Lego has become ridiculously expensive recently, which will eat into future ROI. I have a feel for what's worth the money and what's not - investment potential notwithstanding. For example, the Saturn V rocket is a bargain at full retail price, and so is the Titanic, actually. I've pretty much the same mindset as @TonyL. Now, I'll buy only the sets that I like. That way, if their future value falls through the floor, I can break them open and enjoy the build ... assuming my visual acuity and digital dexterity don't let me down.
I have visions of building a Lego Town, now that I've amassed a dozen modular buildings, three of the fairground sets (rollercoaster, carousel & ferris wheel) and plenty of Speed Champions cars.