I like the deity restrictions, in fact I was thinking along those lines too. I don't see how a deity from another world would have the power to bless something inside Ravenloft's plane anyway. It would really be all about regional faith and conversions. Just a bit of fun flavour for those that enjoy playing those faiths, not unfair at all to those who come through the mists following foreign deities, since that is what the player chose to do, and having a weapon or item blessed should be just as difficult and, if not more special than enchanting.
My thoughts were that the blessing thing would be exactly the same mechanics as enchanting, but just a different setting/method. Your idea of rare, comparable trophies is a good thing to think on. Perhaps a drop could be possible on bosses in difficult dungeons. This would require a party, so there is more player involvement and interaction there, and also the possibility of more than one person wanting the trophy, which while that could lead to some OOC annoyances, (hopefully not the case), it could create some interesting role play also. While that isn't quite on the same level as spending all that time harvesting re-agents, levelling alchemy and then risking it all on a dice roll, it's the best I can come up with for the moment.