Don't think too much can be read into the number of WSO's in the Surveillance world apart from the fact that the RAF needs somewhere to put it's WSO's given the reduction in 2 seat Sqns for them to command. The civilian career comment has a certain amount of truth (although I had no problems commmanding a pilot level salary outside), but much has to do with the fact that staff officer posts are generally manned by Navs.
Finally, although WSO's do well to Wg Cdr/Gp Capt level, they rapidly hit a glass ceiling and there are very very few 2 star navs (more engineers infact).