I think you are doing a great job. One thing I've learned from reading the forums is that greys are really individual. Some birds are social, some aren't, some are shy, some are aggressive, some cling to their cage, others strive to get out etc. etc.
I totally understand what you are saying and appreciate all the efforts you are making to socialize your bird. Your post also indicates that you know that may never happen. Then again, reading here has also shown me that greys can make some pretty remarkable progress after a long time, just when you least expect it!