How far is too far?

This is completely off topic, so do tell me if I've wondered too far from the pack, but as well as reading Systematic Theology on what the Bible teaches about the Bible I've been reading, well, the Bible which is great, but also confusing at times. So I know I'd find it helpful every now and then to throw out questions and thrash them around a little to try and clear things up in my mind. How does that sound? I don't know what the best way of doing it is, but for now I've labeled this Genesis (because the question is from Genesis) and I trust you'll think of something clever!

Genesis 22 - where Abraham almost sacrifices Isaac - is generally considered to be pretty amazing, which it is. There are extra details, though, which take a little more rooting out to discover. In v5, Abraham seems to think that Isaac will be coming back from the mountain with him - and we now know that he "considered that God was able even to raise him from the dead" - so his trust in God's ability to keep his promises was amazingly strong. Moreover, his prophetic (20:7) statement in v8, "God will provide for himself the lamb" reaches far beyond finding a ram caught in a thicket to Jesus who was sacrificed in our place. And there are other details that could be made into points. For example, Isaac could be made into a foreshadowing of Jesus in that he had to carry his own wood up the mountain (v6) as Jesus carried his cross-piece and the three day journey could be the three days in the tomb - figuratively Isaac 'died' when God told Abraham to sacrifice him, and 'undied' when God told Abraham not to.

But now I think I'm just getting silly. And this, really, is the question: how far is too far when it comes to making points from details? How much allegory is too much? How do you know when you've gone beyond what the author intended and are making your own extrapolations?

What say you?

PS. for another example, I started thinking about this slightly earlier in Genesis at chapter 19 (the destruction of Sodom). Where the only reference in Genesis to unleavened bread comes up (v3) and the angels make everyone blind (the last plauge on Egypt before the passover). Was Moses dropping these hints to tie together this story with the rescue from Egypt, or am I going crazy?

PPS. I realise this may be an impossible question to answer, so sorry for being quite random. It's just been bugging me for a few days, and any insight would be great!