There is a value to increasing the number of TOR nodes you use, it just depends how paranoid you are.
Take for example a scenario in which some large operation is running a big number of nodes, in such a way that they manage to occupy 20% of the tor network. Since you randomly choose the nodes you use, if you use only two nodes, there is a 4% chance that both of them are controlled by that organization (20% * 20%), using more will decrease that chance. For example, if you use 10 than the chances all nodes are controlled by that organization is 0.2^10, which is much lower. However, you will suffer a much greater latency.
But if you are that paranoid, you should also take into considaration that there are other ways to track your tor traffic other than owning all the nodes you go through.
For example, one can track your behaviour when surfing through the TOR network (mouse movment speed, distance between keystrokes) to the point it is unique to your behaviour and than compare it to your surfing behaviour without the TOR network.
Another way is to track the timing or size of packets when packets go in to the network and compare it to packets that go out. TOR has ways to help obfuscate it by batching packets together before sending them to their next destination, but again, that has an effect on your latency as well.