Ok, I am using currently Romancing Saga 3 (well, mostly) monster sprites for my game. But, honestly I aint feeling them so much anymore. They look really similar to the FF 3/6 monster sprites. Which, by the way people over use to death. I have decided to switch to FF 4 and FF 5. Yes I know, they are still FF monsters, but not used even close to as much as FF 3/6 ones. Well, thats about it. I just felt I wanted to share this with you guys (for what ever reason, I dunno.)
YOU need to do what you think is best. However, there are other games and resources besides FF to work from so you have a wide choice of monsters. If you want really creepy ones enter http://v-r.hp.infoseek.co.jp/ into the Wayback Machine- while the monsters there were originally made for 2K and XP some face to the side so they may work in RM2k3.
I agree. I believe that a game should always offer something that you can't get anywhere else. Or at very least offer it in a unique and original way. So if you're tired of seeing the monster sets and believe them to be over used than imagine what the players must feel like. If you feel your project will benefit from these tweaks than go for it. If you're still torn, than make a back up of your project before changing the sprites. If it feels weird or wrong then just restore the previous version and be done with it. To be honest a lot of the best things in my project I stumbled across by accident or just by trying several things.