I know this issue has come up in the past so I'm very excited to announce this new feature, which is live now.
As some of you have previously pointed out, with the 3D Showcase link, it's possible/easy to extract the Space ID, change the link ever so slightly and end up on the Space page with access to Workshop. Although unauthorized users could never make any changes in Workshop, the community brought it to our attention that even being able to see hidden scans and 360 Views was considered a security and/or privacy issue. A valid point, indeed.
For that reason, it gives me great pleasure to let you know this is no longer the case. In order to access Workshop, you now have to be an authorized user of that account. The launch button is still there, but Workshop will not complete loading if you're not logged into your account. of course, by "your account" I mean the account to which the Space belongs.