Yes, price and speed.
Additionally,
-pad number and CLB number, BlockRAM number is usually less;
- package footprints are different (but i did not verify every package);
-projects for small devices (less than ~300 000 gates) can be designed by free Webpack;
- as a rule, Virtex is fabricated by high end technology, Spartan is by one but step back.
Spartan has same logic cell arthitecture with virtex. Different is virtex has more embedded memory and faster running speed, also virtex has more DCM blocks and supports more IO standards.