Sounds like you both need to have a little heart to heart and discuss options. I don't think it would be unreasonable to ask waiting a bit longer with the skiing until you can find a way to be somewhat financially secure, but I don't think you should quit enjoying the things you love either. Please keep in mind this is from my perspective, here's a little bit of info just so you know where I'm coming from.
I trashed myself pretty well over the years and ended up with 20 some surgeries (shoulders, knee, elbows, wrist, ankle, back). My goal was to return to pre-injury competetive levels. I was laid up most of the time from 98-01, and spent another year after that working on getting into decent shape again. I know what you're going through with chronic pain from an injury, but don't let it get you down. If your wife had her ACL replaced and she's ready to go ski again, I think she should go for it as long as she's gotten herself in good condition. Some extra conditioning and sports specific training would be a good idea, but I completely understand her need to get back out there and enjoy it. I also understand your worries, it's not a good position to be in and if anything happens you could be really screwed financially. Chronic pain can really get you into a rut and cause depression. If you're just being realistsic about your situation, great; just remember to find things to do you enjoy and not get into too much of a doom and gloom outlook.
As far as I am concerned, I started over from scratch in '02, including a new career which is quite physical at times, and I feel better than ever. I'll be 41 next month. I'm a little more cautious and less reckless than I used to be, lost that I'm invincible attitude a bit; but I still play hard and love every minute of it. No fear, enjoying it all.
Life is too good and too short not to enjoy it, and the only thing you can't get back is time. JMHO