This problem would be very easy for LL to fix.
Each sim can support 31680 avatar/hours of usage per month. So all LL need to do is impose a monthly usage cap that is proportional to a parcel size, e.g. if you have quarter of a sim, you get 7920 avatar/hours of use per month before your usage is capped by LL.
This would mean that even if you only had a tiny parcel, you could still have an occasional party with 40 guests, but that no single parcel would have the ability to hog all the sim resources 24/7.