Air Conditioning - mini split recommendation

I currently live in a house that is now about 2700 sq. ft. A few years after I moved in, I added a room appx 280 sq. ft. Even before this, the HAV unit was not large enough for the house. Also, the house, which was a spec house, was not ducted very well. The master BR stayed cold while the rest of the house was about 5 to 7 degrees warmer. My HAV man installed a larger compressor and air handler (Goodman) to the tune of about $4000, and I am still not happy. I was thinking of placing a mini splint unit in the addition, which will hopefully help cool the air in the remainder of the house--I hope. Since the addition stays warm in the summer and cool in the winter, I asked him about a mini split heat pump. He recommended a 24K BTU unit to the tune of appx. $1800. Before I throw more money into this spec house, I would really appreciate some advice. I also spent appx. $800 getting more insulation blown into the attic (the house is about 16 years old), but I can't tell that it helped a bit. Thanks for your help.

Id spend the money on fixing the duct work to make the rest of the home more comfortable. Also two ton sounds like a lot for a room that is 16x17. How about a small PTAC unit. But they should be able to get more air by fixing duct.