Yes, we just bought a set of metric impact swivels, cheap ones and I already had 18,,, only one I own but even at 30$ there was some consensus here as to,,, we made it this far without them??? ha. Like the ratcheting wrench, they are nice but in our scheme common combo is the ticket, the cheaper in some cases the better as it promotes purchase. At a dollar or 2 a piece its not a gut wrenching descision to throw another wrench at a problem. Same for a few cheap impact sockets. Buy 2 or 3 of the sizes we use the most on occasion for total investment of 10$.
We usually leave the last socket we use on a drive tool. I was being cheap and passed on a couple 6$ tape measures at Sears, they had heavy blades, 1x25. When I used to do customer work added one to bills on occasion, had a pretty good stash but it looks a little bare out there and am making a couple hang up deals for razor knives.
I really dont group tools by set but by use/frequency/duty cycle. My pickup is a good example. I cant remember the last time I really "didnt have" ,,,, where I didnt have a version of every wrench they made to where I couldnt do what I set out to do with pretty basic. On pickup I carry 1/2 drive shallow chrome sockets and a set of deep impacts with a 9/16 shallow and a 15mm tossed in. Proto ratchet, MIT breaker bar, couple extensions, battery or electric impact.