To CGI or Not to CGI?

“Improving” Classic Who stories with new CGI/updated effects is not a new concept, but it is getting more attention with the Blu-ray releases. What do you think of this practice? Is it a nice-to-have extra? A must-have to get Modern Who-only fans on board? Or is it unforgivable to even think of replacing our favorite wobbly sets with new-fangled effects?