Due to my limited knowledge on Nissans, I can only give you some information for your reference.
1. About Throttle Body service: at Toyota dealer, it is part of a standard 30k service, called "fuel induction and throttle body service". It requires a kit of three bottle/can of chemicals, namely fuel system cleaner, throttle plate & air intake cleaner and top engine cleaner. These things are from Toyota distribution center, not what the dealers want to use. Nissan service procedures should be similar. Since you van is only 30k, you can omit this service. If you want to DIY, you can buy a bottle of good feul system cleaner and put it in the feul tank; buy a can of throttle body cleaner and take off the intake pipe and spray clean the throttle body and plate. At Toyota dealer rags wetted with the cleaner are used in the cleaning job. But Nissan recommends not to touch the throttle plate, so just spray it clean; the purpose of the top engine clean is to help reduce valve carbon build-up & improve combustion burn, I guess you do not have the right tool - adapter, to perform it, so just forget it. You even can forget it at next 30k. Then why they recommend this shit? This is a preventive service. It is to help maintain correct combustion and reduce emission. Valves with heavy carbon deposite will tend to make system run lean and increase the combustion temperature and may increase the production of nitric oxide (NOx). At first 30k, without this service should not do any harm to your van.
2. Transmission Flush $130: good price compared at about $200 at the area I am located. The question is wether is needed. Please check the Owner's Manual for the recommended service schedual. For older Toyota cars, 30k requires factory minimum transmission drain and fill, or upgrade to transmission flush. But since 08 most models do not require transmission flush service until 100k. I do not know about 08 Nissan Quest. I can not help with this item.
3. Coolant Flush $100: I do not think necessary. The cheapest coolant in the market can last 50k miles. Even if the coolant in your van is worse than the cheapest, still you only need a coolant drain and fill. Only when different coolant mixed (pink mixed with green. etc.) should a flush is necessary. Check your Owner's Manual for service information.
By the way, these items are basically money makers for the dealer. You need to check carefully what your car really needs.
Hope can help you save a few bucks.
Good luck.
