Most of time, the phrase 以后还得了 is often used for negative connotations. It's along the line of (我们不应该放任不管，不然)以后还得了.
It implies that we should do something/take some measures to stop it developing or it would grow to the degree of being big/serious later.
But in some specific context, it can imply positive, so we need to look into the specific context to ...
不 = not
得 = able to
了 = end --> be contained
不得了 (can't be contained): desperately serious; disastrous; extremely; exceedingly
乱堆的木材一着火就不得了 = Once the messily piled up timber caught fire, it (can't be contained) will be disastrous
他的快球这么强，再学会曲线球 就不得了 = His fastball is so strong if he learned curveball he will be (can't be contained) unstoppable
In a casual situation, 看一看 and 瞧一瞧 are quite the same and totally interchangeable. They are both acceptable in Mandarin, and Mandarin is valid for any Mandarin speaker, so we don't have to be too sensitive about the regional difference.
However, there exist situations where 看 and 瞧 have different meanings.
Watch the television.
[It can mean, "Have ...