The difference between Gold and 1K is that you have higher priority in everything and a few more perks (like award fees waved, global, regional upgrades, ...)

1. If you were waitlisted for upgrade to LHR, then it was put in the system correctly. United has a fare bucked "R" that it uses to allot upgrade seats. It only puts seats in "R" that its revenue management team determines it cannot sell. Sometimes upgrades don't clear if they sell the seats. Also the $100 is not a United thing- rather a tax for upgrades by the UK.

2. That stinks about getting a bad agent. The 1K line is pretty good about being efficient; in the future if you get a bad agent, hang up and call again.

3. You join the upgrade list when you're checked in for the flight. This just means that people checked in after you with higher status (Global Services) and they deserve higher priority. Sorry you missed your upgrade.

There will always be someone in the world with higher status than you or a higher fare than you when playing the upgrade game. If you want to fly in First, the only way to guarantee it is pay for it. United is a business at the end of the day. That is the same regardless of airline and status tier.