More can only be added via a major update. Up until recently we were only allowed 50 items in a personal space. We can now have 100 - excluding active items.
At some point we may be able to have even more. But it will require another major update (core client).
Personal spaces have a baked in ceiling max of 100 available furnishing slots. If you are decorating with active items they may greatly reduce the available slot space you can furnish with.
For example, if you have 75 items and the active loot cam which once took up 22 slots but now only takes up 16 (I believe I can't remember so someone may want to chime in if I'm wrong)..then you would only have space for 8 more items
Unfortunately that's not much of a possibility, most of PlayStation Home's PS Plus exclusive features are all customization matter.
PlayStation Plus members should get extra slots for spaces.
Getting extra slots takes more memory allocation that PlayStation Home doesn't have, it can't be done very easily unless like earlier stated there was perhaps a core update to allow such improvement.
At the moment Home appears to be at it's limit for furniture slots and I'm doubtful much more can be added regardless of being a PS Plus member or not.
If you go to the Furniture Store and find Game Mechanics, we have table and chair combos that are 4 chairs and a table, but only take up 3 slots. More utility using as few slots as possible is a goal of ours.
Don't we all wish to get more memory slot.
Some of my places feel empty that it's like someone came & robbed me ! LOL
Hopefully the PS4 will have more memory slot.... If PSHome get release to the new system