I actually think offering lounge access at 40 or 70 nights is a joke - I will have comfortably re-qualified as a Diamond with 120,000 points yet I have only stayed myself 20-odd nights (with a further 12 overlapping nights which were my kids room on holiday)... so I have spend the cash, yet someone can stay 40 nights at a HIX or similar, and likely spent far less (as reward nights also qualify, but overlapping stays don't) and they will get lounge access as a reward...
They shouldn't base it just on nights, but also on $$$