I find in my thinking that I divvy up the lenses into actual users vs. play things.
If I'm smart and control my LBA, the play things cannot cost a lot. Actual users can.
In practice, I've discovered the above is BS
In theory my 16-45 suffices for the ultra wide, and a 70-210 for my infrequent tele needs. In AF, the 43 is the fast small lens... so what am I doing with a DA70 in addition?
In practice, I'm having too much fun - and using - my motley crew of cheap MF lenses as to make the first list less 'actual users' than 'backstop coverage' lenses. Once I figured out that great quality can be cheap, I threw out any 'lens road map'!
I play with macro, and like the ability of close focus at least. The 16-45 is pretty good with that... but I have several MF macro or close focus lenses, plus a bellows, plus extension tubes... which means I can get pretty serious about macro before I'm tempted to spend big bucks.
Of course, I'm a wierdo nerdy trad pentaxian, and I freely admit this. The main reason I went to Pentax digital is the ability to near-seamlessly do this vintage lens stuff. I fully admire and admit the benefits of modern lens obsession