Hang on as long as you can but if it really is a stretch financially, you'll have to sell the Z
I have a 10 month old, luckily wife has an SUV and I actually just had to pick up a 3rd car (09 VW Golf City as a winter beater/daycare mobile on a short term lease takeover)
The Z is kind of an inconvenience but wife is staying positive lol. I gotta work a bit harder to justify that 3rd car for us lol.
I have to agree though, I think getting the kids into the back seat of a two seater will grow old vey fast. Wife had a 328 XI sedan before and it was annoying getting him into the back...so she got an X5 now.
Doesn't mean I still wouldn't do it just so I could still drive a sporty car
lol