I believe that as all starts to settle after the last several years, Marwell is to find its feet once again..
The place truly does have very much potential - it'd be good to see this realised, though recent things seem to indicate the place is moving in a nice direction.
I think earlier on I was also very much one of the 'sky-is-falling' crowd that Marwell would never relive former glory, and that whatever came before was simply greater than how Marwell is today.
And, maybe it will be that Marwell will never quite again live up to how a number of nostalgiacs seemingly would so desire it to - but I still look forward to what is to come either way. My visit to Marwell in 2021 was what I would call rather pleasant - perhaps helped because incidentally there was no major Lego display that year.
But if anything, I believe there is one thing that Marwell ought to look at - the old Tropical World, which still seems to stand today. Of course, Tropical World as it was is certainly in no competence compared to the new-fangled Tropical House Marwell has now - but I still do somewhat hope that this building is converted into something new, whatever that may be.
@felis silvestris I could be wrong, but I don't believe there is an outdoor pool. Based on Google Maps imagery of the enclosure, it looks like there is a mud wallow in the outdoor area, as well as the indoor pools.