I'm also an ageing PC builder! I also have a 3570K computer, which has been fantastic for the 7 years or so since I built it.
You don't mention the type of cooler you're using, but 4Ghz is a pretty mild overclock for a 3570K. You could try upping the overclock to 4.4 or 4.5Ghz very easily with a good cooler, which might help in some of your games, if you're CPU limited. It's also a free 'upgrade'
How are you measuring the amount of VRAM being used in your games? A lot of games will actually allocate all of the VRAM available on a GPU, but may not actually make use of all of it. Still, it may well be worth upgrading the GPU to something a bit more up to date. I'm using a 1070 with my 3570K system which works well at 2560x1440, although at that res I'm most likely to be GPU limited in games.