I agree with you Steve. I was talking to a geezer a few years ago about adding disc mounts to ti frames (I had a '96 Marin Team Ti at the time) and he'd sent his Hei Hei back to the States (Ti sports I guess?) to have a complete new back end with a disc mount put on. As I remember it was costing in the region of £350.00! He said he loved his bike and couldn't see himself parting with it, just wanted to run discs.
I ended up having a disc tab fabricated and installed on the Marin (I know, sacrilege!) by GB Prestige in Dronfield, cost £100 but I had to tidy up the pigeon-shit welding and re-grind/file the disc tab into a nicer shape. You ever worked with ti? It's bloody tough! Much harder to drill and file than steel!
I sold the frame a year later to a friend who still uses it to this day without any problems at all.
I agree too easy to spoil the look of the back end by getting a Disk mount welded on. To be honest a decent V-Brake on the back with a disk up front works a treat anyway. I'll post pics of my beauty once I get the new decals on it.