Well, to answer my own question, yes I does make a big difference!
I tried it out restarting the same save file a few times and building different stations.
In this case, it was costing:
1-platform, 160m – 0.9k per month maintenance
2-platform, 160m – 1.3k per month
2-platform, 240m – 2.2k per month
…so it seems longer stations may increase the maintenance more than having extra platforms. Not sure if this is across the board, but in this case it certainly seems to be.