Now THAT's a username! (Not that there's anything wrong with that.

)
Way to demonstrate the 3 R's with your Metro. You've probably already discovered there are more than a couple of other mechanically inclined members here (Metro owners and others) who have rescued older, efficient cars from a date with the crusher and cut their energy use.
I'd say 50 mpg in construction in falling temperatures is decent, and you're right to expect higher numbers in ideal conditions.
Welcome to the forum.