Malta and Crete are not totally irrelevant, and neither are Sardinia/Sicily.
IPC value on them would not help much. Okinawa and Formosa have IPC value and that doesn’t have much of any effect.
It depends on your opponent and game situation. These islands can all be HUGE.
BTW Malta is 6 spaces from Russia, which has come into play at times for me. Bomber can reach Moscow in one move from Malta
Sardinia/Sicily can be important - Allied aircraft staging from there can attack Rome and get back, without an airbase, and can’t be invaded by Euro armies overland…. Also potential landing places. You don’t have to actually land on an island for it to be useful - they can make attack moves with aircraft legal.
No, Malta doesn’t reflect its historical significance most times, but this is true of many other places as well, and the opposite is also true.