We normally try and organise things like you suggest , get the first cheap train in the morning (after 930ish) and when coming back later have dinner before getting the train back so to get those cheaper late trains. Work doesn't always allow for this though.
As for going up for the footie...I always dread looking at the trains in advance as Southern (or SouthWest) have endless engineering works at the weekends meaning a 90 Min journey turns into a 2.5 hour journey with some soul destroying bus replacement service. There has even been Sat or Sun where both Southern AND South West have EWorks.
I suppose at least I have the option of another operator, unlike you?
When you are on the cheap tickets it is good value, and I'd rather do the train than drive.