I find, for me, that variety is key. I get very frustrated with wearing the same few pairs of shoes over and over again. I prefer to have a black and tan option in the styles I wear most often, and having a traditional style in a standout colour is both amusing and invigorating to me (knee high slouchy boots, ropers). I also am kinda persnickity about shaft height and what it's worn with (I cannot stand tall boots under pants of any variety, for example, and short boots with dresses or skirts are still difficult for me).
We've had a LOT of rain this year, and I found a number of very cute rain boots that work with different outfits and slogging through mud when camping on clearance late in the season, so I snapped them up - for me, if I'm having to wear rain boots every day, I want variety in them, too. If I can get them, at a good price, to meet my needs, I think that's reasonable.
I think what makes a good boot collection is what works best for *you*. Some of us love booties, and others love a high boot but can't get one across our calves without alteration. For me, it's covering contengencies of erratic weather (temps range from 5F to 105F, with high humidity, copious rain and ice in the winter, and lots of red clay mud) with enough variety to keep me from getting annoyed WHILE keeping me comfortable (I really cannot stand being cold, at all, for any reason, for example).
