Purchasing the IIIg depends on your shooting style. Otherwise it becomes a vanity piece.
The IIIg does offer two sets of frame lines and a modern shutter speed progression - but other than that, the ergonomics are pure 1930's.
I purchased my current IIIg - after selling one and then missing it. The IIIg is lighter and more compact than the Leica M3 that I use for road trips. Personally, I like the way a Barnack fits my hand and I don't mind being limited to screw mount lenses, of which I have plenty. YMMV
I did try out a Leica/Minolta CL - which is a more practical camera, but it didn't feel as robust as the IIIg and its RF wasn't as precise.
If I were in your shoes, I'd bite the bullet, give the IIIg a try and if doesn't fit your shooting style, sell it here.