Upgrades into domestic first are also not that common if you have the lowest tier, so you'd might get one every tenth flight or less or more, nobody knows. What you get is free Main Cabin Extra at Check-In... however, the best spots are already taken by then by *O Sapphire+.

There's no point in going for AA this year if you want to target another airline next year. When would you then use the perks you've gained? That's the main "issue" with FFPs... you need to more or less stick to an alliance to receive the perks.