Lots to think about there.
I really like the aptus rendering, but it is slow to use and slow in terms of ISO. Something is wrong with the firewire on mine, maybe it could be repaired, (does anyone do that?) I think being able to shoot tethered would help with some of the issues. Since it wouldn't require taking the card out to see the images.
I mostly shoot still life in studio and in the wild. I've been relegating my 22 to personal work, and using my a7 for client work. I'd love to add it in more. Some of my work is here -- https://www.flickr.com/photos/23072609@N04/
So from your reply some of your priorities would be:
- Better ISO range
- Faster/Easier tethering
- Faster interface
- Good Live View (very useful for still life)
None of those will be accomplished by repairing your Aptus 22, which is likely cost-prohibitive. However, I'd suggest working with the dealer you purchased it from on testing it; it's very possible that the firewire hardware isn't actually defective and the issue is cabling, power, setting, firmware, or software related (the first two being the most likely). Whether you keep it or not it's useful to know if the firewire is working or not.
To get better ISO, faster/easier tethering, and a faster interface I'd suggest any of the backs that are in a modern chassis and have USB connectivity. In the Team Phase One lineup, at the low end this would mean a Credo 40 or refurb IQ140 (above your stated price range, but within the same ballpark). At the high end this would mean an IQ3 100mp (
quite far out of your stated price range).
To get better live view you'd need a CMOS back which would mean, within the Team Phase One lineup, a Credo 50 or refurb IQ150 at minimum.
For what you shoot, based on your FlickR feed I'd also say that a tech camera would be a great additional tool to have. You could look around maybe for a Cambo Wide DS with 35XL or similar last-generation tech camera kit that might come in at only $3k-$4k if you could find one; just be aware that such lenses may not hold up for future higher res backs if you continue upgrading in the future.
From what I'm reading here I'd suggest staying put and saving up another year or two. That way you'll have a less restrictive budget, and the price of the backs that would represent meaningful upgrades to your needs will be less expensive.