Did I buy at the wrong time? (a57 vs a58)

No, I think you did good.  If I was buying today (bought a couple months back) knowing what I knew now back then, I wouldn't have changed my mind and still bought the A57.  There's a lot of lightning in the A57's bottle, much of which was improved upon in some way from the previous model version.  Other than possibly the new sensor (which may be good but has yet to be meaningfully tested), features/specs really didn't improve in the A58 (and unfortunately more than a few features regressed).

It seems that Sony intends to dumb down the A5x series a bit and push those wanting more into higher series bodies.