I definitely hear you on this. I'm probably terribly cheap, but I generally won't buy a physical game until I've either A) verified that there will not be any DLC for it that I'll care about or B) the Complete/GOTY version comes out. Even then, I generally tend to only grab physical games at $20-$30 new and digital games at <= $5. Usually, by the time a digital game I'm interested in hits that price point, it's been out for a bit, so a physical release seems unlikely (though, it does happen some times - e.g. Limbo/Inside). Regardless, it sounds like you're having greater success at maintaining a physical library, so I'm a little jealous :D
I'd probably come across as cheap too. I see it as efficient. Here's the thing - my backlog would likely keep me busy for at least a year or two if I bought nothing else. Obviously this won't be the case as I've yet to get Last of Us 2, Doom Eternal, FF7 remake, etc. Wanna try Tsushima. Why pay $60 if I can play the backlog in the meantime and maybe get 2 or 3 of these games for the same cost as one now. Black Friday can be quite nice some years.
I try not to worry about DLC. My games are long enough, ha. Sure I miss a lot of side content for any number of games but the truth is I can't play everything no matter how hard I try. Even free stuff gets passed on sometimes.
Yup. $30-$35 seems to be the sweet spot as far as low price while still being readily available in great condition. Some games go lower, sometimes you're stuck with one gnarled copy off the used rack. A lot depends on how popular it is. You're right it's tough, you just never know if a physical version may happen. If digital hits rock bottom price first then ok whatever, I can live with that. Half the time I wait so long I end up forgetting about the game which probably isn't so bad since I have plenty to choose from.