While I don't know about the quality of any of the Hiltons in Thailand or Australia--you might check the threads on specific properties here in FT or the reviews in Tripadvisor--I fully agree that these are great destinations. The sand and scene won't be quite as pristine as the Maldives, and with the possible exception of the new Conrad Koh Samui the hotels won't be as great, but there are many beautiful beaches. Both countries will be cheaper than the Maldives, Thailand in particular. In Australia English is obviously what's spoken, but in Thailand you can get by fine in English as well.

As you may or may not know, Australia even has some urban beach scenes in cities like Melbourne and especially Sydney. Not nearly as relaxed as remote tropical settings, but kind of fun.

That being said, I do again suggest you read the reviews of specific properties, since some might present more crowded scenes and beaches than what you'd (understandably) want if your preference is places like the Maldives or Seychelles. And the advice you're getting here (including from me) assumes that a few weeks in just one place would be too much for you. Given that you loved doing exactly that at the Conrad Maldives, perhaps you should consider finding just one or two places where you'd want to hang out.

One other thought, especially if you're going as late as March, is to check what other hotel chains might have nice properties in these places and apply for their credit cards, together with sign-up or initial spend bonuses.