I think a lot of tools are like fishing lures, designed more to catch fisherman than fish. Of course everyone's needs are different depending on the type of work you plan to do. I realize that my choice of tools isn't necessarily the best for everyone, but I have done a lot of different machining jobs and have had to figure out how to best hang on to things. I like things simple, rugged, and versatile. If you're not doing production speed should be the last item on the list to satisfy.
There are just some basic tools and accessories for lathes and mills that let you do 99% of anything you might need to do and if you're a careful shopper can be had at reasonable cost. On a lathe things like thread files, a good lathe flat file, live tailstock centers, steady rests, etc all make life easier. On a mills/drills items such as small right angle plates, V blocks, a decent vise, etc are really handy. I like mill vises without ears, the Kurt I use is ground flat and square on all sides and can be clamped down on its bottom, sides, or end.