Depends entirely on what the niche is, or what the topic in Wikipedia is.
If you're in ecommerce and sell fashion, chances are that if you don't have any jquery image sliders, your more successful competitors do.
But you don't generally go to wikipedia to look at the pictures.
It depends on whether the pictures are appropriate. On Wikipedia, artists out of copyright often have a wide range of paintings on the pages devoted to them. I do sometimes go to Wikipedia specifically to look at these. Wikipedia also offers some iconic classic paintings (some, eg, by Botticelli) in a variety of file sizes, often quite large. Check out also the pages for Cezanne and Gaugin, eg,... maybe not the best selections, but respectable.
Many SEO blogs are offering some good graphics to illustrate their stories... and while some are merely offering what I think is cutesy junk, I think the illustrative graphics on sites where the graphics are used appropriately are already a ranking factor, perhaps so implicit in the story telling that we don't even notice it.
Video also is becoming a major component of some web reporting. You can't look at a news site without encountering video. Shopping sites are offering video product demonstrations, and competition will force these videos to get better over time. Don't forget audio files in the media mix.
If your competitor is using lot of images/videos, can you still outrank him?
Depends on how engaging and compelling your text content is, vs how compelling your competitor's content is, along with his video and images if they help move the written story along. What the audience wants can be a big factor.
Sadly, many companies just do video because it's on a check-list, and I think that's a big mistake. Make sure there's a point to it, and that it's done well... or well enough.
