I have no particular advice on software (I use the GIMP when I have to do something with photos, but that’s because I’ve been too cheap to buy Windows, let alone Photoshop), but yes, following the Muse of whatever media strikes your fancy is a Good Thing. (It’s not like you do this art stuff for the money....)

If you ever come across a good (by which I mean, well-curated) source of clip art, I would be interested in a link. I have long envied the campy photos that Kathy Sierra used to illustrate her blog, back when she had a blog.