In article , says...

If AQ had them for some time, they'd have used them by now. And would not
have been wasting their time trying to foment "dirty bomb" plots.

Not especially.

Even al qaeda has a sense of public relations.

Blowing up innocent civilians in Western countries is acceptable to most
of the people al qaeda are targeting as their "audience'; i.e.,
jihadists against the West.

However, a good argument could be made that use of a nuke against a
Western country would loose al qaeda the support of many currently
moderate Middle Eastern/Southwest Asia countries, and potentially hurt
their image with the typical man on (their) street.

It would also definitely change the opinion of many of the moderate
countries world-wide that are unhappy with the US and its recent
actions; it could swing world-wide opinion back similiar to that of just
after 9/11 when the US enjoyed nearly world-wide support.

In short, it could hurt their 'cause' far more than help it.