Think of all the things you have wanted to learn but never had the time... well now you will have lots of spare time
Hajj this year is in the winter so at least its cool enough to go out during the day, there are some great private beaches north of the city, some are associated with hotels and are free for people staying in that hotel, others are around Euro 10 per day. Your layovers might be too short for scuba diving, but at least try snorkling or go on a boat dive, all day for about Euro 40.
Restaurants cater for all tastes and pockets, they range from American food chains like Fridays, Ruby Tuesdays, Chillies, Fuddruckers, Mc D, BurgerKing, Hardees, to French Italian Japanese Chinese Indonesian Thai South African Indian Pakistani Turkish Lebanese etc.... I would say that compared to European prices these are cheap, 3 course meal in one of the nicest French restaurants costs about Euro 19, whilst 4 meals in the Indonesian restaurant cost about Euro 15. Even the large hotel chains can have some good buffet deals.
Shopping, once again take your pick, from the old gold souk downtown to about 100 malls, Jeddahites love to shop.
If you are more adventurous, then go visit Taif, 90 miles south east of Jeddah, the drive to quite amazing but the city itself has nothing to offer. A 3 day trip to Madain Saleh is also worthwhile, but you must stick to the roads and not follow the train line. (This was where some French expatriates were attacked and brutally murderedlast year).
Do's and Don't.... Do bring a large amount of patience
Dont drive!!!
As for bars and nightclubs.... its not as dry as advertised
Mutt