I liked the sparks feature in Google+ but was clearly not as observant as a friend who asked for a fix to make his sparks reappear. It seems that sparks has now been integrated with the new search option and are not listed so prominently as they were before.
If you search for terms in Google+ you will get a list of results that can then be refined to:
So the sparks haven’t completely disappeared.
There is also a save search option. Clicking this adds the search terms to the left side navigation in Google+