The spread between Hyatt Platinum & Diamond is pretty big. However, Starwood also only have two elite tiers (Gold & Platinum). Hilton Gold is very good (for a non-top tier level) with the free breakfast (even Starwood Platinum doesn't have that feature). I think your strategy is sound (Hilton Gold - which a lot of people don't put much additional value in Hilton Diamond except for the Diamond force for bookings and Hyatt Diamond).

I've been a Hyatt Diamond for 8 years - complimentary (not confirmed in advance either with a cert or booked with points) suite upgrades are very rare (only 2-3x in 8 years - not counting the properties with lots of suites that routinely upgrade Diamonds to suites - in my case PH DC, former PH SF, former PH LA).