Vectors are a lot of work for no gain. They make everything more complicated, especially if you want an efficient CDR operation, and there's just no reason for it. Yes, your code might compile a little faster, but Lisp code is generally compiled incrementally anyway, so compile cycles tend to be measured in milliseconds already. There's just no point in speeding it up any further.

Conclusions: Lisp is invariably implemented in terms of conses rather than vectors for a wide variety of reasons, which were discussed in detail in the preceding post. No one of these multiple reasons stands out as the "killer advantage". Vectors just turn out to be the death of a thousand complexities, whereas conses are simple, extremely flexible, and sufficiently efficient for the purpose. A great deal of additional insight can be gained by actually implementing Lisp both ways and experiencing the differences first hand.