It's OK Photon... I believe in your invisible dragon!
I would have no problem buying a house like that, especially if it were at a discount. That is not to say I am discounting entirely the idea of spooks (in fact I hang around a few people who think they can contact them) but that it wouldn't be important enough to influence my decision. In fact, if the property was discounted, it'd probably influence my decision onto the 'pro' buying side.
If there truly were a ghost living with me, it might be kind of interesting. I'm really not scared of stuff like that at all. Real or not, ghosts can't hurt you.