Castlevania: Aria of Sorrow

No not really. There is no point to having more then one of each soul.

Yeah if you have defeated the HeadHunter boss in the Inner Quarters, which I'm sure you have, for every soul you get from that point on makes it's soul a little stronger. What I mean is that the Head Hunter soul increases your stats by a bit, right? SO for every soul you get, after getting the Head Hunter soul, the amount the HH soul increases your stats by goes up a little. For example, if you start out with him only giving you 2+ per stat (except for LCK), at the end of the game if you have craploads of souls in your inventory, the amount the soul will give to each of your stats would be maybe like 30+. So collecting multiple souls of no matter what is sometimes always useful. Note the after the HH soul increases the stats by 32+ ( or 36+ sorry I forgot ) it will stop increasing the stats. If you have 256 souls ( even multiple souls from multiple enemies ) that is the max amount of souls you can have before its stops increasing your stats. Also note the HH soul does NOT need to be eqipped in order to increase its stas.

The only reason to get multiple souls is to power up the headhunter soul because the stat gain is based off the number of souls you have.

Yes you can if you did got their soul again