Dan,
All I can tell you is to keep trying.
Your prior experience doing other types of maintenance certainly isn't wasted, but isn't going to be seen as particularly valueable as an aircraft mechanic. There are some exceptions; the firm where you mentioned applying picked up a particularly valueable mechanic with a background as an auto body man; he could planish and english wheel and fiberglass about anything, and paint. In his case, it was a big boon.
For engineering purposes, unless you have a DAR, then adhere very closely to the manufacturers approved data and FAA publications, even if you think you can do it better. Trying to do it better, or work outside the approved data, is the quickest way to become unemployed I know of, short of decking the boss. (Haven't tried it yet, but have certainly been tempted). Employment aside, it's a sure way to run afoul of the FAA and the courts, so avoid that at all costs.
Your prior experience working while going to A&P school is helpful, but more for your own benifit than as a selling point to an employer. The facility you visited, for example, is a repair station that employes a large number of uncertificated mechanics. Many of these individuals, even without certification, will have far more experience in heavy maintenance and other areas than any 147 graduate, and will be extremely qualified when going for their practical test. If your prior experience had been cylinder changes, mag timing, structural repairs, and the like, it would be far more significant than oil changes and rotating tires (which are really preventative maintenance, as opposed to the real nitty gritty).
Approach employers very humbly. It feels like you have lots of experience right now, but an employer will NOT see it that way. Coming to a shop looking for work with the attitude that you're heads and shoulders above the next guy, will seem like a 600 hour commercial pilot seeking work claiming to be "high time." You see my point.
Keep beating the bushes. The work will be there. Don't worry about that. It may take some time, but it's there. Make sure you send a follow up letter to Mr. Mikus or Dubry, and tell them you're still interested, and would like every consideration. Then keep following up. They are always hiring, and you'll get more experience, and more diverse experience at that one place, than any other place in this country...because there is no other place remotely close to being like it. Good luck!!