Linlithgow for me - the only UK track that has staged league racing in the last 30 years that I missed out on visiting. The previous miss was Coatbridge.
Also Landshut in Germany as I have been there (29 years ago) and it was postponed. Still a chance of getting back there though!
Being either London/South East based since I started watching Speedway I'm sorry to have missed out on West Ham, Rayleigh, Romford and Reading Tilehurst.