Prior interest: slight
As a Mario Kart fan, my heart started to race for a moment when I saw a cartoon racer on the demo list.
Odds of purchase: none
Mario Kart sets the standard for kart racers. (It even supplies the genre name.) On the opposite end of the spectrum sit barely-playable cash-ins like M&M's Kart Racing. Mario Kart sells year in and year out because everyone who plays the game loves it and wants a copy. Shovelware succeeds because by the time anyone plays the game, it's too late. Releasing a demo sends the signal that Racers' Islands sits closer to Mario Kart than to the M&M game, but playing the demo reveals the opposite. Unlike retail shovelware, which can rely on box art, junky WiiWare titles need decent-looking screenshots and trailers to attract sales. It's a wonder that Racers' Islands: Crazy Racers bothered to release a free version that demonstrates how poorly the game controls. It honestly felt like I was driving not a race car, but a unicycle.
This seems to me the worst case scenario for the game's publisher. (But I'm glad they let us feel how poor the game plays without spending the cash.)