Went to Santa Cruz yesterday despite my broken toe. I wanted a day away from the computer, work, and thinking about either. It is important to maintain a work/life balance, and sometimes just getting away is the best prescription. I hobbled around all day, putting 14,790 steps (7.27 miles) on my FitBit, but enjoying the sun and fresh air.
The Boardwalk is a "tourist mecca," so anyone traveling there during the summer, or holidays, should expect crowds. It is also a bit on the pricey side. You can purchase a wristband that gets you unlimited rides and attractions, and/or a card that lets you do the same and to play midway games. One of the interesting things I found with the midway games is that children under 12 get an automatic win just for playing. I think this is a great idea, and certainly fair to the parents who are spending money for their kids to entertain themselves. It keeps the kids happy, and of course encourages them to spend more money, but at least you are always getting something for the money you shell out. There are also non midway games such as miniature golf, pool, shuffle board, etc.
The rides themselves, are on par with most fair style rides, but not at the level of the big amusement parks. There are a few roller coasters, spinning rides, and a couple drop rides, as well as a sky tram and a few others. But don't forget the Pacific Ocean, wild life, and all the scenery and of course food. According to Google most people spend 3 1/2 hours here, but you could easily spend an entire day if you take it slow and take in everything the location has to offer. There are also Friday night concerts and Wednesday night free movies on the beach at certain times of the year. There is also copious amounts of beach activities including volleyball and barbecues. Lots of people bring tents or canopies and spend the day on the beach as well as visiting the boardwalk.
The downtown area is less than a one mile walk away, and has a lot of really great restaurants and shops. As for accommodations, they are everywhere and range in price, but are within the affordable range. I've written reviews for three of them that can be found on TripAdvisor and/or Google. If you don't want to stay close to the beach there is a fantastic Hilton hotel about 10 minutes away by car on 17. I highly recommend it.
There are also a few other beaches in the area, as well as surfing, kite flying, and a various boat trip offerings. The red wood forests are within a short car drive away as well. I think about four days would give you the time you need to do everything at a relaxed pace.
And make sure to enjoy the sunset!