With a splenectomy, platelet counts will remain high forever.
However, it will come down to the 400-450K levels over a period of time.
The funny thing is that despite the higher number of platelets, I have seen no changes to my clotting time whatsoever - if, anything, I believe that my clotting time may have increased. Post TX or blood drawing, I have to always take a dry cotton swab for coagulation to happen. A swab dipped in alcohol keeps the blood flowing!
Not on Aspirin, but have been taking Vitamin E, as Andy also mentioned.
Cheers
Poirot