I think it's all relative. Would I want to be a GB member? Hell no. However for them, it may well be the best life they could achieve. They have a level of security that most people do not - they needn't worry about their housing, food, healthcare. They live on well manicured grounds and get to travel the world with no cost. They don't own mansions, but they have access to picturesque "regional translation offices" and I'm sure they're not staying in 1-star motels while traveling. They clearly either use the money they control to purchase luxuries for themselves (watches that cost 5-figures, gold rings, etc) or they use their power to secure many "gifts."
Security is an immensely valuable thing, and these guys have it. They may have to live by the moral code that they've set up, but I'm certain that there are ways around that for men in their position. Honestly I didn't find the JW moral code to be all that oppressive (well, not once I got married...) and they probably aren't bothered by the parts of it that they follow. Their friends might be conditional, but they're probably all bordering on sociopaths (being conservative) and probably enjoy the power that they wield over their "friends." Their travel may be for JW events in most cases, but there are a great many people who would love to go and talk in front of an enthralled audience of thousands of adoring fans anytime they travel. I'm sure the JW related events are a very different experience as a GB member - not the drudgery that we're used to. So a vacation centered around a convention might be quite enjoyable in that position.
They may not get the absolute best in life, but lets face it - if not for the cult they'd be nothing close to movie stars, so it's not really a worthwhile comparison. The life of a GB member is probably the absolute best life that any of them could attain. Just because I'd kill myself doesn't mean that they're absolutely not in it for themselves. Whether conscious or not, I believe that most, if not all, of them are definitely keeping the cult going in part to maintain their lifestyle.