Is the TSH lower? You have hashimotos - there is no clear link to platelet increase that I know of but it appears that you are developing ET and it may be auto-immune (not from Hashi but given that you have one auto-immune process you may be more likely to get another).
Normally it is recommended to remove thyroid when nodules get bigger for its more susceptible to cancer with growth.
The cause of essential thrombocytosis is unknown. Secondary thrombocytosis may develop as a result of, acute hemorrhage or infection , anemia, arthritis and other chronic inflammations, cancer, exercise, iron deficiency, medication (antithyroid), csteoporosis, removal of the spleen (splenectomy), polycythemia vera (a disorder affecting other red blood cells, as well as platelets), stress, or surgery.
In May 06 the TSH was 1.38, Free T4 1.06. Thank you for your opinion.