Originally I just had one budgie, Bubbles. I loved him, but he never really bonded to me, so we got Misfit to keep him company and give him the companionship he clearly wanted. The difference in him when we got her was amazing. He was so much more content. It was definitely worth getting her for him, and although neither were exactly tame, we could still handle them both and take them in and out the cage. Now we have four and they're really happy together. They're not tame, but they'll step up to go in and out the cage, and we can handle them to check wings and trim nails without too much fuss - and if they fly off and get lost, they coming running to our hands to be "rescued", lol.
When we got the cockatiels, we got two because I work nine hours, and my bf is at uni so his timetables always changing, so we got two so they could keep each other company. They haven't bonded, possibly because they were hand raised and we got them just after weaning, but maybe not. I find though, that they do keep each other company during the day, and when we take them places (like on holiday) they are always together which I'm sure reduces stress for them, as they have each other as a constant, when we can't always be there.
At some point in the future though, I want to get a Maxi Pionus. I haven't yet decided whether I would get one or two. I won't really be in a position to decide that until I'm ready to get one, in a few years time.