I'd love to see a Tholian or a Gorn or something of that nature.
Ambassador Tezrene is one of my favourite characters from the novels. I know it would be hard to have a regular character 7 feet tall, several feet long with a prehensile scorpion tale all dressed up in a spun gold suit but still, it would be nice.
The real trick seems making sure someone can act through the suit or CGI or whatever it is. It can be done, though! Look at Kosh on Babylon 5
or Ood Sigma on Doctor Who
. Maybe some kind of encounter suit for a Medusan, complete with vodor?