I help people I know with basic car repair from my house, I have a friend who drives a 2007 Sienna with 215000kms, they have codes for all 6 spark plugs, I told them to ask a real mechanic what they think because in my opinion if all 6 of the spark plugs start having issues at the same time, there has to be something wrong with the engine. The mechanic told them to replace all 6 spark plugs, what do you think? Would it be a waste for them to spend $500 to replace the spark plugs?

This car has a lot of issues too like the battery, A/C etc. to fix all the issues would be definitely more than the value of the car but they are willing to fix it if that means the car would last a couple more years without major issues.