I agree with what you said but only to a very limited extent. Buying brand new car is good for people who absolutely have no knowledge of cars, no time to spare and last but not least zero risk taker.
However, I believe in buying 4-5-year-old luxury marque at the price of brand new Camry or Accord and drive for 2 years with minimum maintenance cost and limited depreciation - unlike when brand new.
All car in my signature is a testament to this theory and I never lost more than 20% in depreciation for 2 years of ownership.
Secondly, when buying slightly used car, you are more free to try new stuff or experiments than fitting the K&N will void the warranty.
I even remember buying a non-working Jeep Grand Cherokee on recovery truck for 5K because it has V8 magnum grunt for off-road and then sold off for 6K after spending 3K to make it in running condition. The project car is always a gamble and more you learn the better you get in taking shots as per your need and expectations.
And sometimes you simply get lucky by chance, in my case I bought 3.0 Pajero for wifey while I was having a 4.5 liter Nissan patrol. Once I sold that Patrol, I thought of testing that 3.0 Pajero in sand and to my surprise I was chasing a modified Jeep Wrangler of a seasoned off-roader in sweihan and that 4x4 never died. After fully testing I started searching for 3.5 liter (my present Pajero) as in that year 3.5 + SWB was extremely rare.
For an offroad project car remember that Power - Weight ratio is king, I even remember maintaining an excel sheet from wikipedia stats of knowing which car has better hp/ton. That's why you see old Nissan Patrol sticking LS1 engines than any other car as it is the lightest shell with reasonable safety aspects to bump up the power to get the best power-weight ratio.