Personally, I can understand the intense curiosity of what you're feeling. No, it doesn't matter since she is your child; yes, you will still love her just the same. But the idea will always be there, just as it had been there for a while now (assuming you gave this a considerable amount of thought, as it is deserved before posting openly on a forum). Personally, I am one who cannot tolerate being in the unknown. I get furious when I find out about things later down the line that I should have know while it was happening. Being under enforced ignorance is something I cannot cope with.
I believe there is nothing wrong with finding out. HOWEVER, I am completely on-board with everyone who have brought up the fragility of family ties that this little string of thought is tangled around. If you can guarantee with no doubts that you can keep all emotions under control OUT of your family core and values, then there is no harm done in finding out. It's just.. time has proven that the human heart and mind do not work this way. Just as you might be certain that uncovering this truth will not affect your emotions now, it is just as likely (if not more so) that you will have planted a ticking time bomb ready to explode further down the line.
30 years has been a long time. That would mean your daughter is 30 years old, an adult woman capable of processing her own thoughts and emotions of her own accord. Ultimately, this is part of her choice too, whether you like to admit it or not. Could you imagine if you were in the same situation in which your father whom you have grown under and followed all your life was doubting the source of your existence? That he went behind your back to make sure you were his? Things like this have a high chance of being found out by your daughter. And I can guarantee, no matter how much you explain to her that this was just to satisfy your own curiosity, she will see it as something you were deliberately looking for to lower her validation, and that of her mother's.
Reflect on yourself and see if you can keep this huge life-changing information from everyone around you. You can literally talk to NO ONE about this. Would you be able to carry this on for the rest of your life while treating your family exactly the same as before? If you can, then by all means, find out to satisfy the nagging within your own mind. But if there is any moment of hesitation, it might be a telltale sign of something you shouldn't be dabbling into.
Rookie Scribe