I for 1 treasure having and keeping HH Diamond (not called Plat), the main reason is that they have been able to get me into Hotels on free nights that were sold-out. Nothing worse then having a ton of pts and not being able to use them.
It also goes along way when staying at a resort or top notch prop, upgrade wise. All in all IMO it pays to do the 28 Stays a yr, which by changing places every night, can be had in no time. Also theres a tier level revolving chart, which means you can requalify via a 12 month period rather than a calander year. In a nut shell that means if you qualified say by Stays, and you had 28 Stays bet 11/1/05 and 10/31/06 you will be a Diamond on 11/1/06. Lets say you have 10 Stays bet 11/1/05 & 12/31/05 and 18 Stays bet 1/1/06 & 10/31/06 then according to ALL other Progs you wont make it since you'll have 10 for '05 and 18 for '06. But HH counts all Credits for a 12 month rolling period.