Don't know yet, but I have a 6 year old daughter with AS and am expecting a son next month. And yes, I did get pregnant on purpose after my daughter's diagnosis. Since I got pregnant, I've had a lot of people ask me "what if the new baby has the same types of issues?". My response has been "Well that would sure make things a lot easier!". I know this may sound odd...but when I really think about it...we have a well established daily schedule, things in our house are modified to reduce sensory input problems, we are used to explaining reasons for everything, all objects "places" are labeled, an hour or more is planned for every meal so food can be organized before eating...ie our whole household is run to be Aspie friendly. I honestly think it may be easier to have another Aspie than to try modify everything so that the house is equally Aspie/NT friendly:)
I guess I also look at it from the standpoint that EVERY child, ASD or NT, is going to have their own personality and their own challenges. I have an NT stepdaughter, and honestly she is a lot harder to deal with than my little Aspie...she knows how to lie and manipulate (something my Aspie is not capable of), as a teenager, her whole life can be turned upside down because a "friend" is having a problem (I imagine my Aspie would just avoid such emotionally charged encounters at that age), the NT has emotional collapses for no apparent reason (Aspie just needs less noise, or had an unscheduled change)...
Plus we have WAY more leverage with the schools to make adjustments for my Aspie's learning style and for accomodations around sensory things, etc. When my NT stepdaughter is having issues, the answer is "she's going to have to deal with it" and that's the end of the discussion. While an IEP is not a fun process, we do get a lot more legal leverage and support from the community and school to adjust the environment to fit our children's needs.
So I guess what I'm saying is...it's all a matter of perspective. Sure you could look at having multiple special needs kids as a burden, but you can also look at it as a blessing:)