You don’t seem to understand that the “shine” left with the clearcoat.
You are going to get less in any event as it gets older, it is simply a matter of how much less. 8 year old car, kept 3 more years is an 11 year old car selling for a few thousand less than now.
You get what you pay for. A $3K paint job won’t be a custom paint job, it won’t even be as good as factory, but it will be shiny and you can wax it every week if you want. I’ve had them paint 2 of my cars. Both turned out pretty well and held up. Same for one my Dad had painted.
By what I can see, the car is worth $12K or so. A 3 year older car is worth maybe $9K. A $10K paint job isn’t worth spending on the car. A $3000 job might worth it if it allows you stop worrying about the car and enjoy it until you sell it.
The options you have are… Just wash it and accept how it looks… Or pony up the $3K and have it painted.