of course that's only on Calypso or Foma or CP. Item points on other places is different. Highest number of item points per estate is on Rocktropia in places like the U apartments, etc. Penthouses up top there have more. Watch out though some places like the shitler or whatever it's called on RT have way fewer item points than anywhere else in game.
An increased amount of item points allows you to have more items on display and for sale at any one time.
+20 item points – 2,000 PED
You can place your items in your estate - for decoration, for safe keeping, or for some functionality they offer. An increased amount of item points allow you to place more items in your estate.
However, it only works on some estates. Mindark refuses to allow upgrades to Foma estates. Also in some rare cases upgrades happened free since Mindark forgot to make the p2p trades when upgrade requests were put in. It's kinda rare, but it has happened a few times. I think they make you make a support case to do the upgrade, schedule a time to make the p2p trade to Mindark rep, and then in a next vu or two it happens. If that p2p trade never happens since player cannot log in at times Mindark rep wants them online, etc. the upgrade just happened anyways since request was sent to the other dept in charge of the estate programming or whatever. Sometimes I guess it's profitable to have hectic schedules.
Also, in some rare cases Plnaet Partner avatars, or avatars close to being affiliated partner or whatever have traded estates for cheaply or freely... or offerend them as event prizes, but it's only happened a time or three. Search is your friend in finding those examples that are publicly known. Entropia Universe is dynamic.