Proper historians whose work doesn't end in "Code" or feature on the History Channel, is there anything of value in the apocryphal texts with regards to the historical figure of Jesus (or even the theology of the first Christians around Jesus)?
The gospel of Thomas is viewed as a source for the saying of Jesus by some scholars, who date it to the first century. Others think it's a later work, dependent on the Synoptics. There are a few extracts from Jewish Christian gospels preserved in writings by later, gentile Christians which can be safely used as a source. (But they're frequently ignored, which is a bit surprising).
Apart from that, theres nothing in the apocrphal gospels which contain any genuine information about Jesus. They're only useful as a source for the gnostics themselves.
No apocryphal texts that I'm away of (as a non professional historian) but there are quite a few secular historical references to a man named Jesus and the things he did. Josephus, a Jewish historian born around 40AD (I think, on phone right now), spoke of a man called Jesus whose conducted was good and had many followers. He goes on to say that this Jesus was condemned to death but his followers claimed to see him alive a few days later. I emphasized the followers claims because Josephus himself did not witness the event but many spoke of it years afterwards.
Another was a Roman historian Tacitus. He too wrote of a Jesus of Nazareth who's followers called themselves Christians and who had spread across the land after his death.
The Jewish Talmud (hardly secular, but at least not Christian) has in Sanhedrin 43 an arrest warrent for Jesus. "Wanted Jesus of Nazareth, he is to be stoned because he has practiced sorcery and enticed Israel to apostasy. If anyone has anything to say in his favor, let him bring it before the great Sanhedrin" Remember the Jews of that time did not believe Jesus was the messiah. This arrest warrent was written before Jesus' crucifixion as the future tense is used.
A few others would be Suetonius and Pliny the Elder (I'd get you more on them, but I'm on my phone right now and info gathering is tough)
Edit: Here's the un-doctored text from Josephus