I'm not sure what the purpose of the room is, other than to show of collected goods. Personally I didn't care much for Harmony of Dissonance and never finished it. Aria of Sorrow is one of my all time favorites, along with it's direct sequel Dawn of Sorrow. I'd say out of the 3 GBA Castlevania games, it's the best of them. Especially when you start playing around with Soul combos.
Some of the Metroidvania style games do feel a bit cookie cutter though, but out of them all, I'd say the best are Aria, Dawn, Ecclesia and Symphony (natch). Ecclesia starts out tough as nails too and when I first got it I didn't get very far. But I went back to it and played all the way through in a few days and was very pleased with it.