I tried to find big sonic differences between a TD-165 and a 160. It is not easy. Probably they are very close.
The TD-160 is built better, with better wooden plinth, a better tonearm, a better motor and a more solid, metal subplatter.
Yet, if the TD-165 is in good working conditions, I would probably go for it: it has more character, more appeal than any Rega Planar 2 or 3.
I've been thinking of replacing my old Thorens TD-165 with a new Rega or Project - thank God I didn't! I would have regretted it for life! I replaced it, but with a TD-160! ;-)
It is also a matter of tastes and practicality: one may like the modern looks more or may have difficulties or lack the time and wish to do all the adjustments a Thorens suspended table needs to run at top performance. A Planar is more "plug and play"...
They are also two different approaches: rigid vs suspended plinth.
Although at the end it might actually be a "sidegrade" more than an upgrade, personally I would do it...
But I would not spend more than $200 for a TD-165 yet to be refurbished and adjusted!