there's roughly two ways to get stronger:
1) improve neural/intramuscular efficiency
2) get bigger
These two work usually together. An extreme example of 1) would be a figure skater who's onyl concern is to push a certain weight/his partner once over his head. He usually doesn't want to get bigger or press more and more weight.
An extreme example of 2) is hard to find. A huge bodybuilder who ONLY does medium reps (whatever that is), never tests his max or even goes out of some 70% comfort zone? I've never seen such a fella.
Think about this: If there'd be a sure way to increase mass, even if it's by adding tissue that is completely useless, competitive bodybuilders would've already discovered it. Hell, some of them inject oil into their body to look a tiny bit bigger on stage!
So far, it seems that 1)+2) are almost always connected and, in rare cases, you can get 1) without a lot of 2). 2) without 1) is more a theoretical thing.
And for your second question: looking "harder" is a bit overrated.
It's first and foremost a question of how much water you carry naturally.
That means: as long as you keep training or even just, you'll get "dryer" as you age.
That's not a good thing, things that age usually die some day (if that's the case with you, go see a doctor!).
You never see a young bodybuilder have that "hard" look, no matter how talented. Older bodybuilders, however, do have the "mature" , "hard muscles look" if bodyfat is in order.
so...don't worry about that stuff, it's from a practical perspective rather useless ("is my mass functional? Is it as hard as it should be?" <- scary stuff).
Unless you are a figure skater.
Then I advise you to go immediately to the coiffeur, fashion & accessories and makeup subforums and trade your secrets with us!