My OH has ground coffee all the time (I have instant) and I always empty the cafetiere onto the bed outside my back door (which has various plants in especially roses) and have done every day for years. They always come up robust and another plant that comes up better than the others in other areas of my garden are the bluebells. I also give my beds a covering of mulch in the Spring. I use Westland Gro-Sure Smart Ground Cover Mulch - 100L bags around £9.00 per bag which lasts me over the growing season and it's good for breaking up clay/heavy soil as well.
Like you priscus, I use the water from boiling my veg in - an old tip from my ex Father in Law in 1967, whether it does any good or not I don't know.