HH Gold is absolutely worth it for free breakfasts.
HH Diamond has a good chance of upgrades at low-end properties (the local Hampton Inn), and a good chance of small upgrades at high-end properties (higher floor, better view, but same room), and a small chance of a big upgrade (suite).
For the amount of $$ it will cost you, obviously it makes sense -- the question is if the shuffle will drive you insane.
Don't be surprised if on your upcoming honeymoon you do not get any upgrade at all, even as a diamond -- as that has happened to me more often than the suite upgrades. (no upgrade at all, not honeymoons!)