£417 for the week is £59 a day, so call it what $85 on the current exchange rate and I think that is pretty good for Planet Hollywood especially factoring in the Friday & Saturday.
I can't remember the month you are going but I do remember it is summer. August sees rates drop considerably because it is deemed too hot for most people so there is serious value to be had then. Question has to be, will you find a rate better than $85 a night (and that includes tax) by leaving it until a few months before travelling? I'm not so sure on this one. I personally would book that deal and stop looking (so as to avoid the pain if you find it cheaper nearer the time).
If you go with PH, make sure you sign up to the A Card (you can do it online or wait until you get there). By doing this you get a lovely booklet of offers including free and BOGOF drinks, free blackjack tournament, free slot pull, money off in food outlets and restaurants and $5 free slot play (amongst other things). Well worth doing it.