Followed instructions but things are even worse. I've lost over half of my coins since updating 2 machines to 1.5.0.7. I assume I made a mistake during the updates.
That sure sounds like you were on a fork chain by using the older wallet. So the coins you "lost" were probably never legit in the first place, but mined on the fork chain and therefore invalid.
Now that you are synced with the chain you shoud be seeing the correct amount of coins. For a more detailled view you can use the command "listaddressbalances 0.1".