My Thambar cost $1380 US without a spot filter. I managed to find the filter for $95 so $1475 US in total.
I honestly don't think you can have a relevant discussion comparing a modern coated 75mm Summilux and a 1930's uncoated, uncorrected (for spherical aberration) lens created specifically for, as Justin put it, "dreamy portraits".
The Thambar is a piece of history designed to do a specific job probably only of interest to collectors. However I will say that I think the effect it produces is way more subtle than anything a soft filter produces. A poor analogy would be comparing a shot taken through a lace curtain to one taken through a gentle mist. The Thambar appears to me to avoid the artificiality I sometimes see in shots though soft filters.
I could however be trying to justify the money I spent on it!!
The Thambar not better just different.
Must remember to buy food and not old lenses, much healthier!!
Kind regards to all.
Steve