I have a non-rules question about upgrading monster types in silver and gold campaign levels.

Once silver level you can upgrade one category to Gold, and the rest to silver. Is it a wise use of Conquest to upgrade both 30XP costing categories to silver in this example? Have you found it is better to spend the XP on other upgrades?

I did read an article somewhere (boardgame geek perhaps) that suggested leaving one category at copper throughout the campaign. Is this a common practice or a decision more dependant on which avatar/plot/hero party you have?

Given the fact that the best way for the OL to win is before the heroes reach his keep. I would spend the 30xp on my plot trying to get to the win condition long before I would spend it on a huminoid upgrade.