In general I find shore excursions to be overpriced for what you get but this expense has to be balanced against the convenience and peace of mind they provide. The trick in deciding which excursions to take is to fully research each destination and examine the excursions offered by the cruise line. In many cases you will find it is possible to basically duplicate the excursions offered using taxis or local transport for a fraction of the price (particularly as it sounds like a number of family members travelling together). Please let me know which ports you are visiting if you want specific advice and I will endeavour to point you in the right direction.