Sounds like you really don't need a new PC, sounds like your son needs a PC. If you have lots of stuff on your current PC that you want to retain, it is going to be a pain to move it to the new PC.

Maybe you should just get your son a new PC. And he probably wants to play high graphics games (when he is not doing schoolwork, of course), have super sounds, and all that good stuff. The software that he needs (for school) might need a bit beefier PC than the one you have now.

I suggest don't try to buy a PC to be future proof. PC technology speeds along too fast, chip sockets change, add-in card slots change, memory slots change, etc, etc.

As stated above, you can get a really good deal, and a very good machine, if you buy last years model. They are plenty fast enough.