Adam Cooper was off when I saw it at the Palace, and it was one of the few occasions when I've found an understudy in a West End show to be rather disappointing, so I think I'll try to see this to finally, hopefully, see him. I'm not booking a year in advance though.
Gosh, saw it in 2000 at the National, the standout performance for me was that of Lina ... wiki tells me it was Rebecca Thornhill! 19 years ago ... Audience at the front were given colourful umbrellas. Great fun. Saw it twice at the Palace too - 2011 says wiki.
Yes to Clare Halse, just right for the cute as a button Cathy. I really liked Dan Burton in Gypsy, he'd be a great Don or Cosmo (Simon Lipkin too tall??).
Clare Halse played Kathy opposite Dan Burton as Don at the Theatre du Chatelet production in Paris a few years back, with Daniel Crossley as Cosmo (reprising his Palace production role). It was great casting and I'd love to see any or all of them in the show again.