Yes, there are some tools to help you. The keywords you need to help you learn more is "traffic shaping." The stock Slackware does come with some of the tools needed for traffic shaping.
As you noticed, I don't think wget directly supports on-the-fly modifications of bandwidth usage. Possibly you could use wget in a wrapper shell script that concurrently checks open TCP connections. If there are no connections then you could restart wget using the -c (continue) option using full bandwidth. Just an idea.