Just to mention GroupSave4 - not sure how much of the Country it covers or if it's off-peak times only - but may be worth checking out for away matches?
If there are 4 adults travelling together (or Group save3 if there are only 3 of you) can be a good deal because 4 (or 3) people travel for the price of 2:
National Rail Enquiries - GroupSave Calendar
It was a bargain the other Sunday for my 16 year old DD and her 15/16 year old friends to go to Thorpe Park by train. Four of them being 16 were considered adults, so we bought a GroupSave4 saving half the fares and then there were a couple of 15 year olds who were charged a quid ('kids for a quid' to London).
Southern Railways wouldn't let us book online but we just went to Brighton station and paid on the day. I do often buy Advance tickets but you don't always want to be restricted to an exact train in case you miss it.
You can book groupsave 4 on the first great western website if you CBA queueing at the station on the day.