Wait you said two games but you listed four

I own a full size Kick (earlier version of Kick Man). Basically the same game but with a different marquee and title screen. The actual cabinet itself doesn't go for much maybe $200 to $300 USD. I think it's an okay game but the game has it's cult following. It would be pretty hard to play without a cabinet since the image is reversed and projected onto a mirror. The trackball is also special since it only spins two way (left and right) as opposed to all directions. I imagine the boardsets wouldn't command much because of these factors and the fact that the complete game doesn't go for much either.
Alex Kid is a fun game similar to Wonder Boy. I actually liked these games because they both were like Adventure Island on the NES (Famicom). I don't know if the board would command much but I think it's definitely worth more than a throw away $20 USD board. If I didn't already have Wonder Boy, I would easily drop $50 for it. Someone offer me $100 for mine but you can't really use this price to gauge the value.
As for Ninja Kids and Robo Wrestling, I've played both of these games but other than that, I've never heard anyone asking for either game. I imagine neither of them are highly sought after so take what you can get for them.
3xChaos
Michael