As in all things in life, I find myself the contrarian.
If the only complaint you have about your current job is the salary and they've now rectified that, I don't see jumping ship. Especially as your partner will soon be able to more than make up any shortfall.
I'm also baffled by the unanimous mentioning of your "loyalty" to the firm by having been offered a new position. Most firms don't lavish employees with raises and promotions without some initiative from the employee. If you don't help management remember what good things you bring to the organization, you usually don't get shown any love from payroll.
It sounds like they've been overlooking the work you've put in and as a consequence they've not been compensating you in proportion to your skill set and good work. IMHO, you've show outstanding "loyalty" by keeping your nose to the grind stone and not making a stink (I assume this is the case).
You've been at the shop long enough to know both the economics and the politics. If they are not in the habit of huge layoffs and retributive back stabbing, I'd accept the counter and let them know explicitly that you love your job, your co workers and the exciting work you've been privileged to perform and look forward to being able to continue to help grow the firm.
Is 12K really enough incentive at your current income/lifestyle to warrant a jump into a situation where the only "known" is you'll be doing less interesting work?
But what do I know, I'd kill to have your current salary