Could Malta have been better fortified before World War II?

Were there pre-war plans to fortify Malta further?

Yes. Britain had plans for further work, and a war beginning in 1942 would have allowed more extensive fortification.

Britain had plans to strengthen Malta before World War II. A war beginning in 1942 would have allowed more extensive fortification of Malta, Singapore, and Hong Kong. Britain would probably also have established a semipermanent presence on Crete. The actual timing of the war curtailed those preparations.