If they are special (they have either +1 MA, +1 AG, or they have rolled a double) yes you keep them, if they didn't roll +1 MA, +1 AG or a double at their 2nd skill fire them and trim your TV. This way you roll more times, you have less TV bloat and you have more chances of rolling a good skill, moreover, if they become too expensive they are not disposable anymore (100 TV on a fragile Stunty player? No thanks). Yes, you can protect a couple of good Skinks (namely the ball carrier and/or the one turner), but protecting all Skinks is hard.Bull. You need 'em all skilled, so if one drops, another can pick up the slack. They're still disposable fodder, but keep 'em running as long as you can.In order to have a TV efficient Lizardmen team you have to skill up your Sauri, and just 1-2 Skinks as ball carrier/one turner, the rest of the Skinks is disposable fodder (thus they must be cheap).
A two skills Skink requires 16 SPPs. With 32 SPPs (16 SPPs each Skink) you have 4 skill rolls (2 per each Skink), while if you stack the same amount (32 SPPs) on a single, not special Skink you have just 3 rolls and less chances of rolling something good.