Would that be unreasonable? Of course anyone can always pay for an executive room, but free lounge access should be a reward for loyalty of those who stay regularly and bring money into the system (I mean hotels, not the corporate - hotels don't have any benefits from someone having a co-branded CC).

Without CC cheats you actually need 60 nights to gain lounge access at Hilton (gold only gives you lounge access sometimes) so 40 would actually be a lower requirement than the present one.