It can be - the older Joe stuff, for instance, can go for a lot. I saw a cover from somewhere before #10 (I think it was #4?) priced at $10K on a dealer's site. It hadn't sold yet, though.
Yup, I collect original art, mostly bought from the artist themselves or through their representatives/agents. I have some more GI Joe related art coming, actually, including a small sketch from Rod Whigham (from the 80s era comics) and Robert Atkins (from the current comics).