You are talking about an "uncontrolled experiment"- let me explain.

You may have accidentally became a "lousy photographer" and not because you are a bad guy, not knowledgeable, or anything bad. If you were getting constantly poorly focused images you may have had a defective camera to begin with, you may have unknowingly experienced an eyesight issue, or may have not been using the autofocus functions on your camera properly. You may have misconstrued camera movement or subject movement blur as focus shortcomings? The only way you could have actually diagnosed the problem was to run controlled tests by manually focusing on a target and then comparing the results to an auto-focused image. Mounting the camera on a sturdy tripod and making certain that the shutter speed was appropriate for any action is another test. If you did not conduct any of these tests and just randomly or indiscriminately sent the camera out for refurbishing- this may have made matters worse and the actual issue was never addressed. If there was no improvement in performance after the repair, you should have taken it up with the repair service immediately.

Even if your old camera was in perfect working order, it is still an old camera and will have lost any significant trade-in or resale value. It is not a bad thing that technology progresses- consider it an advantage to be able to avail yourself of better up-to-date gear.

If you are still finding an alarming percentage of out of focus or blurred images with your new camera, make certain that the autofocus function is set for the appropriate mode for the type of work you are doing- check into the manual and the camera's menu for these settings. Brush up on your depth of field theory especially when working with longer focal lengths at wide apertures and shooting wildlife etc.

Your new camera, if used judiciously, should provide excellent sharpness. Some folks around this forum are so preoccupied with acutance that one might think they are exhibiting their images on the Jumbotron at the local arena or producing photo-murals and billboards. Many are never even making substantially large prints. Some folks are quick to categorize older gear as junk, paperweights and door stops, etc, while in fact, they were decent in their era and have just outlived their usefulness and have been replaced by better offerings from the engineers, manufacturers and the retailers.

Enjoy your new camera. If you have time, run a few controlled tests as I have outlined and make sure everything is OK while the warranty is still in force. If it all checks out, just watch your technique as to AF settings, DOP, and shutter speed. Make certain that the AF is set to hone in on your subject and lock the focus in before re-composing. If you are handholding your camera in difficult conditions, a good investment might be in a sturdy grip, L-bracket or monopod. These accessors help reinforce steadiness and in maintaining precise focus