Re: Aikido for all or one...
The "Japanese Culture" is not so clear cut. Many people in Japan study in other arts and dojos as an "open secret"- Done, but not talked about.
After 15 years of practicing, you are more than ready and capable of experiencing other styles and arts so as to integrate them into your own unique expression of budo. There is no good reason for your teacher to be so locked in to one way only for the students.
My own personal training began to make quantum leaps after I attended the Aiki Expo. Not only did I begin some really serious growth as a martial artist, but more importantly, I was able to begin to better grasp what my Aikido teacher was doing so that I could be a better student of his.
I run my own dojo now and I still train weekly with my original teacher (Imaizumi Sensei). I also train in and teach a style of Karate- Shindoryu (training in Japan several times a year directly under Ushiro Sensei), and train with Dan Harden as often as I can. I still look to experience other styles and teachers. I expose my students to my teachers, talk about what influences me and allow them to develop their own paths.
Life is short, so why allow other people to box you in?