Currently the tag creation threshold is quite low; as per the privileges page:
150 create tags Add new tags to the site
which if you look at the main SO privileges pagemain SO privileges page you see it is significantly reduced (ie by a factor of ten):
1500 create tags Add new tags to the site
Any external users if they have a reasonable level of respectability will start of with 101 rep here; getting 50 rep is very easy - one good answer basically. So I see no need or benefit to even consider lowering it at all.
If a user with less rep than 150 wants to tag something they can just put it in as a notation at the bottom of their question and a user with sufficient privileges will get to it pretty quick - if it took more than 2 hours I would be very surprised.