Sam, the Sefer Chasidim describes Ayin Hara as being akin to Kishuf. He says this regarding Tevilas Nashim with someone else around, IIRC.
The Ben Ish Chai makes the analogy to taking medicine too often. It will stop helping and it would take more effort to get rid of the decease. The same applies to being extra busy with Segulos to get rid of Ayin Hara.
Although the Rambam’s view on Sheidim has absolutely nothing to do with Ayin Hara, we do see that he ignores it in the Sugya of Shutfin Sheratzu Laasos Mechitza.