You need more info before getting a $3K repair job. The leaking valve cover isn’t a big deal. If the leak is very small and not affecting anything you might just let it be. A top off of oil every few months is cheap.
The steering rack needs to be addressed. All steering racks “seep” especially in 10+ year old cars. Is this a real leak? Are you seeing spots on the garage floor? Or, puddles of power steering fluid where you park the car? A little “seepage” could be normal and the rack might last for a long time as it is. If you have to top off your power steering more than every 6 months you likely have a problem. If you aren’t adding power steering fluid every few months then you should monitor the problem and if, or when, the leaking gets worse deal with it then.
Lots of parts on a 10+ year old car can be tired simply from years of use and miles driven. A new power steering rack fits this category. A new one will give you years of service. Your car is old and full of “tired” parts. If you keep it you’ll need to figure on spending about $2,000 a year replacing tired parts (in addition to new brakes, tires, struts, etc.) and some down time while the car is in the shop for repairs. Alternators, radiators, heater cores, AC condensors, bunches of sensors, catalytic converters, yadda yadda, can all just be wearing out and need replacing. This doesn’t mean you have a bad Sienna, it means you have an old Sienna.
If you want a dependable, never in the shop for repairs vehicle then you might need to shop for a new mini van. If you can live with some repair bills you need to find a good mechanic that will charge a lot less than the Toyota dealer service dept. doing equal quality work.