We know many +1 versions and version names are mostly esoteric for all purposes. For example Linux Kernel is "forever" 2.6 (from 2004, and the previous releases are +0.2 every two years, so in 1998 you will probably get installed in your distro a 2.0 kernel, in 2000 a 2.2, in 2002 a 2.4, etc.) and not changed for a long time and 1.6.0 brings little changes compared to 1.5.7 version.
NaroCAD tries to keep the cadence of a new release at every 3 weeks (and we focus to do development for first three weeks) and we mostly consider a line of releases and at every new release we will add a 0.0.1 to its number.
Anyway, as people we judge version numbers. Windows 7 even is like a new Explorer and a Windows Vista SP2 kernel, we consider Windows 7 as being "vastly superior" to Vista bad reputation.
So we did jump to 1.6 line as we considered that if you did not like the 1.5.0, it worth the upgrade. Doing a bit of cherry picking, you will find that 1.6 will have back the updater, will have a smoother experience all over the place, a faster hinter (both UI wise and how is computed internally), you have gizmos. So if you refrained to use NaroCAD as it was missing this or that feature, was an invitation just to check if it does really gets better.
So in short what should be to learn: we do development incrementally, we try to make all builds stable (yet some specific tools lack on it, we love crash reports, and if we can reproduce we work hard to fix those tools, or rewrite them to be easier to use and to make more sense). Also we do at every around 3 weeks a new release, if you will like to know if you are ready to upgrade, try this blog to get the announcement and to see if new features make you love those tools and if they do, you're more than welcome to update.
At the end, we want to increase the version number to you to know that it worth the upgrade, if you had a 1.5.0 like release, and was something you dislike (who knows, maybe 1.6 it will be the case for you) and as you may see that this development of 1.6.1 will not fully fill your needs (we cannot rewrite all NaroCAD in 3 weeks), you can certainly try 1.7.x and you will likely be more than impressed. We also have an updater that makes it easier to you to be up-to-date so you're encouraged to test releases, and every crash will make for us possible to test and fix your problems.