No official trade in program, especially for a pair bought on the second hand market. But you are right, I think the last MSRP for these before going out of production was about $2400 a pair.
If we use the price history of the 2.3 and 2.4 as a guide, the new 1.7's will probably sell for between $2500 and $3k. And used 1.6's will probably drop from an average of $1400 to $1200. So you'd be comparing a new pair of 1.7's for perhaps $2750 and a used pair of 1.6's for perhaps $1200.
Not an apples to apples comparison, of course: one is used and older tech, one is new, and newer tech, and includes a warranty, etc.
Full disclosure: While I love my 1.6's I too felt the need like several other owners to pair them with a good sub. I bought a secondhand SW1 (=SS2) for the market price of about $1400, and use the Thiel passive outboard "crossover" (it really isn't, it's really just an integrator) with very good results.