So long as the time spent reading it and writing it is insignificant, I'd suggest leaving the file as it is. It's nice to be able to be able to edit the file without worrying about breaking a serialization format.
If reading and writing the file costs enough time to be worth looking at serialization, then I'd use serialization. But in that event, if it's a file you read often but edit infrequently, then I'd keep the text file as the 'master' so you can edit it and then run your serializer against it to generate the file you'd read frequently.
When your only tool is a hammer, all problems look like your thumb.