I have taken similar steps to those mentioned above. 35 mm, 6x4.5, 6x7, 4x5, 8x10. I feel that I learned a lot with the 4x5, but find myself wanting to shoot more 8x10. I have an Agfa/Ansco that I got from Midwest Photo.
If you have the opportunity to check out other people's gear, do so. I never had that chance. I am going to start doing some alt-process printing in the near future and that's why I decided to get the 8x10.