It is sad that your entire LA quilting "mojo" is tainted by one machine. The problems you describe having that killed your love of quilting is most definitely NOT the norm for all LA brands. You have a sizable amount invested in your LA if it is computerized. Rather than investing in yet another machine that may yet prove to be another disappointment to you because it doesn't do everything you want it to or has tension issues or whatever you may wish to give your LA one more chance. Find a thread and batting combo that does not cause as much tension issues as you are currently having (which BTW is NOT normal for any LA unless it is defective). You may be using the LA manufacturer's recommended thread but there may be threads that play nicer.
It is too bad you didn't find a good LA machine to begin with so your feeling of LAing wouldn't be so tainted. I love my LA and I would never quilt any other way. I do not have to recheck tension after a few inches of quilting. Unless I have 100% cotton that is very linty in the bobbin. That does give me fits due to a blob of lint getting lodged in my bobbin tension spring and causing problems almost every time I run a linty cotton both top and bottom. Not all cottons are this bad but many are. I do check with every bobbin change and every top thread change. Perhaps if you switched to 100% poly thread in both top and bobbin you wouldn't be having so many issues with tension. Prewound magnaglide bobbins are also a way to avoid tension issues. Or as Dunster mentioned you may just have a lemon machine but after 3 years there isn't much the manufacturer will do about it. BTW I also quilt on an Innova.