Harder to find out this info than I expected... I've found an online history essay that talks of Wales as being "without even a town large enough to attract an opportunistic urban middle class" (
http://www.britannia.com/wales/whist1.html
) at around this time - union with England having done much damage to the confidence and identity of Wales and the Welsh.
Elsewhere Cardiff (which only grew large in the 19th century) is described as small and humble (with a thriving sideline in piracy!).
There's an exhaustive list of fairs and markets with brief descriptions of populations of larger towns up to 1516 (ie a bit early) at:
http://www.history.ac.uk/cmh/gaz/wales.html
If you *really* need the info, you may need to get hold of The Cambridge Urban History of Britain. Volume II: 1540--1840. Peter Clark, editor. Cambridge University Press. �90.00. 906 pages. ISBN 0-521-43141-7. That should answer all your questions!