Yes you can use Express Ride access as many times as you want. However they have been known to limit the number of consecutive times they allow you to go on Spider-man and Hulk in busy times.
If you go during a slow time, you may want to go through the queues as they do enhance the storyline (particularly on Spider-man)
Depending on the time of the year, you will get soaked on the Popeye and Blutos and Ripsaw Falls. They can turn off some of the effect in the cooler months. Sometimes ponchos help and you will see other people wearing them. I suggest that you bring a change of clothes/shoes.
The bonus deal is a great deal. Anyone can buy this pass online and there are specials with the onsite hotels. The pass allows you to go to USF and IOA for up to 7 days and paying the equivelent to a 2 day pass. This pass will allow you to enjoy your vacation without killing yourself to see everything.