Mystery Box has been discussed on soooooo many occasions and generally it's felt it could be much better, of course putting it politely!!!
When you first start the game, getting a bit of free cash was good but once you start levelling up the amounts given on days 1-4 are tiny, almost not even worth it.
And when you get to day 5, it is extremely hit and miss, in one of my towns I got SVT and the lemon tree fairly quickly but the other I waited for ages but they did eventually come. Generally, when you get brown fences, large hedges and small domes of money you do seem to wonder what the point of it really is.
Just one of the many aspects of the game that could do with improving especially as you level up, what is the point of being given gifts of such little value when say as a level 30 plus player and getting over $30k or more a day?
None IMO.