The overhead is no more than swapping out the cards in the wallet every 3 months and try to remember what the categories are. That's not even necessarily if you regularly use digital payments (and of course if the merchants support that).
(And I believe most people never hit that $1500 cap in specific category. If you do, like, spending $500 on restaurant/Amazon/Costco a month is like nothing to you, ignore everything I say)
I'd say the overhead is much much lower than things like "digital coupons" offered by grocery stores -- those are truly aimed at low income shoppers who are willing to spend time doing that.
I’ve got an Amazon Visa that gives me 5% back on Amazon purchases, 2% on gas and restaurants, and 1% on everything else. Rewards redeem on Amazon so effectively as good as cash.
