I spent a year training at hombu dojo a long time ago, and I go back to Japan every year or so for a couple weeks.I always train at hombu when I am in Tokyo, as well as at my teacher's dojo.
My experience with hombu dojo is that it is very different from other aikido dojos because it is such a big place with so many people and so many classes going on. The last I heard they had over a thousand students training there. My experience is that hombu dojo is mainly focused on providing training for it's practitioners, and does not expend very much energy on visitors. Generally, people talk very little during training, and in almost all of the classes you keep the same partner for the whole hour. In addition, its Japan, which means most of the Japanese are not going to speak English.
Hombu dojo gets a huge number of visitors passing through, so what happens is that the people that train there every day tend to train with people they know, especially since they are going to have the same partner for the whole class.It takes being there for a while before people start to take an interest in you. Hombu has so many people training, and each time slot tends to have different people, that you could just train every day for years with the daily practitioners there and never get to know everybody.
So you have to put it in perspective. If your home dojo had multiple visitors coming to class every day, many of whom didn't speak the same language as you, how much time and energy would you invest in training with or teaching them, especially if you knew a whole new batch would be coming through tomorrow, and the next day, and the day after. Hombu dojo practitioners tend to come in, train with the people they know, and head out after class afterwards. It's never been a very social or immediately friendly place, in my experience. And it definitely takes some adjusting to, when you are used to the regular, normal sized dojo where everyone knows each other and you change partners every technique.
Could they make it more visitor friendly? Probably, but with the amount of visitors they get, it would take a large investment in human resources that they don't seem to have. Changing the one partner per class system would probably help, but that is a different discussion.
Now, I like training at hombu dojo. I like the quiet, intense, focused training. It's rare that I don't leave the hour long class pretty tired. Of course it's going to depend on who you get as a partner, but where else are you going to get a high level six or seventh dan partner training with you for an hour. Each trip I usually get to train a couple of times with partners who have very high level aikido. Even when I get someone as a partner who I don't know, which is probably about half the time, I usually find that the majority of my training partners are pretty good and fun to train with. Needless to say, the teachers are very good. I do find it less relaxed than training at my teacher's dojo, or my home dojo, because at hombu I never can be sure what I am going to get, partner wise, for an hour, and training can be very intense. But I get almost always get a lot out of it. Oh, and when I lived in Japan and was a practitioner at hombu dojo, I didn't train with visitors I didn't know either.