Were the Bajoran wormhole effects created with CGI? It'll be an added cost if they had to recreate all those scenes to stand up to HD, since there were plenty of them even in the early seasons.
Weren't there just two stock elements - the wormhole flaring open/shut (flipped for ΓQ scenes), and the more rarely seen "traversing the wormhole" background - that make up 95% of the wormhole shots between them?
Similarly, Odo very rarely shapeshifted when you look at it. It's a unique-each-time effect, but not an especially common one.