The only game that actually needs a remake is Simon's Quest. A lot can be done to that game. Aside from new graphics(No older-than-the-internet RoB/SotN graphics like everyone seems to want. They've been used enough! Some actual new graphics, please!) and remixed music, the mansions can be longer, better designed, and each mansion can have different music and a boss. The townspeople can also talk like normal, sane, and educated people.
Some things can stay like level 5 being the limit, classic controls(same old CV1/CV2/CV3/etc style), and lack of abilities like the double jump. Having the mobility of a character like Alucard and a double jump would just ruin the game.
Also, a Haunted Castle remake would probably be good.