Hi
Dick. You can get your old number back if 1. It is still available. 2. you have an AMA licence with yuor old number on it. Just send in the application with a note and a copy of the old lic. It worked for me after 22 years. 
There was a period where AMA used to recycle old membership numbers. I joined AMA during the 1960s when I was a youth but let it lapse during my college years. A few years later at one of the trade shows, I asked Vince Mankowski about rejoining. He said I should be able to get my original number back as AMA had gone back to their original practice of assigning only unique numbers to new members.
That said, AMA is not unlike any other organization having to compete for discretionary leisure dollars these days. A brutal economy and recent fiscal/monetary policies of enabling primarily the wealthy have devastated what was once a thriving middle class. I can attest as recently as 2002, my professional career and personal wealth were both in far better shape than today.
Sadly, I've had to drop several organizations and SIGs I formerly finacially supported. I'm having to work longer hours, my spouse has been forced to reenter the workforce and I'm finding precious little time for modeling or many of the other recreational activities I used to enjoy.
Demographics have also changed. The rapid emergence of small, affordable and largely pre-built park flyers have seen full AMA participation take a hit. They don't need a sanctioned field requiring AMA membership to fly their "toys". I now have as many unassembled ARFs still in boxes on the shelves because I can't break away from the higher priorities in life.
Just look at today's kids. There is so much more pressure on them to achieve success at an early age they have to commit to grueling sports programs, tackle more difficult courses in school and are straddled with MUCH more homework than I have had to complete 45 years ago.
I'm not sure AMA can reverse what is, in reality, a national social/economic trend.