Platinum would give you lounge access on international itineraries (Europe, S America, Mexico City and Asia). You'd also have a much better chance of upgrades clearing compared to being Gold.

AA gives Golds and Platinums four 500 mile e-upgrades (fka "stickers") for every 10k miles flown, so that's equal to at least 20% of your domestic flying. You earn them on AA/Oneworld miles flown and you can only use them on domestic flights (50 states, Canada, Mexico, Central America and Caribbean). Is platinum worth the extra money? Only you can answer that one.