Well, yes, more precise information is always going to make your decisions easier, so of course less makes it harder. That's not necessarily a bad thing though; perhaps your DM is just running the kind of game where you need to make those calls based off something diagetic to the game, like their combat descriptions ("You shoot the orc square in the chest but the arrow shatters harmlessly on his armor!") or monster research or something. Or perhaps it's the kind of game that thrives on drama, and you just gotta take your shots sometimes and let the dice fall where they may.

And yeah, theoretically it feels bad to waste a buff on an enemy you'd never be able to actually hit, but because you don't know the numbers, you don't know you could never hit. You're faced with a big scary monster, you try to hit it and can't, you run away. The arc of that encounter is the same regardless of which abilities you used. It only becomes relevant if the DM decides to hit you with another encounter, which presumably they only do if they think your lacking-that-ability would make for another exciting narrative moment. In which case, you'd only be screwing yourself out of that dramatic moment if you'd conserved your ability. It all just depends on what kind of game you're at, whether it prioritizes the gamist mechanical rewards or the narratavist dramatic rewards.

Likewise, sometimes you're going to "waste" your buff on some overkill, but you won't know that either; you'll simply be told "Bardman McBardo's inspiring music gives you the vigor you need to waste that guy" and get to feel good about winning your encounter. The emotions average out.