I doubt it. 

Early typewriter keys were made of glass, metal and paper. 

Later typewriter keys were made of plastic. Not sure what kind, but I doubt it's poisonous. They wouldn't have lasted this long otherwise. 

Unless you're eating them or something, that is.
 

I've been readhing a lot about people using silicone spray to rejuvenate (soften) hard or old rubber. How well does this work? 

From what I've read, it appears to have some success, although it's a messy process. I'm currently testing it on the platen of my typewriter (an 80+year-old antique) to see if it'll soften it up for better typing. 

One should point out, during WWII, typewriter manufacture all but ceased. Underwood and Royal all but stopped producing typewriters for the period 1942-1945. What VERY FEW typewriters they DID produce were all for the military. If you wanted one for yourself, you had to fill out a permit of some kind, if I remember rightly. 

Are you talking about the padding underneath the typebar heads, which they rest on when they're not being used? 

If you remove it, I doubt it'll affect the typewriter action. But it will make it noisier (typebar heads clattering on the typewriter frame and such). You can replace it if you need to. A strip of rubber or thick felt will do the job. 

Thanks for the suggestions, guys. I would like a Lettera 22 or 32 if I can get it. or a RQD. 

I want something that looks nice. That's strong. Easy to carry around and easy to use. Something robust which won't pack up if I'm too rough with it. Nothing big and chunky.