Bowie 24 bit remasters....

are these superior to the older Ryko versions with bonus tracks?
Yes but mostly a marginal step up rather than a massive one.
I would agree with Ben,
The Ryko's were brightly lit remasters, and are worth more used because of the bonus tracks. The newer remasters did away with bonus tracks and only offer very slight sound improvement.
The 30th anniversary editions of Ziggy & Aladdin Sane are newer and much better remasters, best CD versions of either album I have deluxe packaging and 2nd bonus disc.
Is there a Remaster of "Let's Dance"?
Actually, I think there are 2 remasters of "Let's Dance." I think EMI remastered Bowie's 80's catalog in the mid-90's (with some bonus tracks) shortly after Rykodisc did his earlier stuff. Then Virgin released a new 24 bit remaster a few years ago.

I've only heard the original CD version of "Let's Dance" (and not recently) so I can't speak to the quality of any of these.
Megasam, thanks for the "heads-up" on the remastered ALADDIN SANE, which was not an available title on the Ryko AU24 (Gold Disc) Bowie series! What is the label of the new 24 bit remastered discs? IMHO that there are many excellent and interesting bonus tracks on the Ryko series. BTW, there is a HUGE sonic improvement on the Ryko GOLD AU24 bit remasters, vs. the standard aluminum Ryko Bowie remastered discs. Are we all talking about the same Ryko discs here?
Don't forget...almost all of Bowie's works will soon be available on SACD. Ziggy Stardust, Let's Dance, and Scary Monsters are all hybrids.
You guys were reading my mind with this post. Was making CDR compilations for a young friend and was going to include some Bowie, but thought, well they are not really audiophile quality. The only upgraded Cd I own of Bowie is a Gold Young Americans. Forgot who produced it, I'd have to dig through my collection. Its at least 10 years old. Im sure its easy to find , but any links to the 30th anniversary and upcoming SACD's will be appreciated. Would love a remastered Diamond Dogs. Also any one know of any improved versions of Earlier Dave Edmunds , Nick Lowe or Iggy Pop realeases ? Thanks.