Trade in value is pretty much the lowest value of a machine. It is not a true representation of value because there are other factors that go into the deal. The dealer knows that this machine has been trouble so they are not going take that on. He would do better selling it privately.
Tier 4. Get use to the fact that these engines are very complicated and that means trouble. As the tier 2 and 3 engines run out, tier 4 will be the only options and you guys are going to hate them. Not only are they $10k more but they will prove to be unreliable and you will have to take them to the dealer to work on them because the software to read the ecm's is proprietary. This is already true with the tier 3 engines.
When people ask why I charge so much for older unit with low hours its because the tier 1 engines are much better then the newer engines. It's going to take a while for you guys to realize this but it will happen.
Your friend is just now getting it.