I personally don't think that the Express Passes are worth it. From what I recall, you can only skip the line for any given ride once, then you have to wait in line with everyone else if you want to go on a ride a second or subsequent time. And as was mentioned, not every ride has the Express Pass. If you did do the passes, I would probably only do them for one day, not two.
The hotel keys, on the other hand, give you unlimited ability to use the Express Pass lines. Such a better deal IF you need to spend the night somewhere anyway. You don't, which is a further complication.
The nice thing about the Express pass is that it has variable pricing with the more crowded days being more expensive. For the time you are looking at, their website shows that the park-hopper option is $32 each day, with the individual parks being more expensive on Sunday than on Monday. In contrast, the park-hopper for Saturday is $56 per person. So I would think that they expect your visit to be during a less crowded time. In briefly playing on their website, it looks like Monday has the minimum pricing for the pass.
If you do decide to buy something, do make sure to check out AAA rates or any other discounts you may be eligible for when making the price comparison. I looked at Loew's website and they have a room at the Royal Pacific for $254 (about $285 after taxes). If you could get that price down through AAA, then the price between the unlimited pass with hotel room and the passes only may be comparable.
Overall, I don't think you need it since you are not traveling at a particularly crowded time. It is nice to have, but in my opinion not worth the cost as you do not otherwise need lodging for the night.