You may be correct, perhaps it would be better to seperate the desired abilities into two groups. One would be for module testing, the other for theme testing:

Module Testing:
1. Strong php background
2. Familiarity with the XOOPS Core Classes / Functions

Theme Testing:
1. Smarty Knowledge
2. CSS Knowledge
3. (should have had this one at the beginning) Ability to test within multiple browsers

Having a strong attention to detail and good communcation skills are secondary, but still important.