I took my 3 month old son to Disney last November. He couldn't ride any of the rides that had height requirements, and slept most of the day. We still rode some of the attractions with height requirements, we simply took turns by utilizing the Single Rider Line, Fast Pass, and/or Rider Swap. While planning the trip, we didn't plan on doing anything with a height requirement, but once there and our son was asleep a lot, we found that it wasn't that big of a deal to take turns, since we were simply waiting for him to wake up anyways.
Something that you should consider is that it is nearly, if not completely, impossible to do EVERYTHING at Disney in a single trip. By removing many of the height restricted attractions from our touring plan, the list of things to do became much more manageable, and we didn't feel like we were missing anything.
That said, both myself and my husband have been to Disney before. We knew then and know now that we will return again...often. We know which attractions we enjoy, and which we don't mind skipping until our children are old enough to enjoy everything.
If you consider Disney a once in a lifetime destination, then it might make sense for you to put off the trip until all your children are old enough to experience everything. However, the list of attractions with height restrictions is much shorter than those that anyone can ride. You could spend the entire day doing only these attractions. If you feel that the value of admission is directly related to the number of headliner attractions you can do, then again, it might make sense for you to put off the trip until all your children can experience everything.
Another consideration is if you have multiple children some of which who meet the height requirements and other who don't. If one child will be very upset if his big brother gets to ride, and he doesn't, then this, obviously, complicates matters. (I was only slightly shorter than my older sister, and she got to ride Space Mountain while I didn't as children, so I understand this dynamic)
If you decide to go, definitely familiarize yourself first, with the rides with height restrictions:
http://www.wdwinfo.com/wdwinfo/height.htm
Second, familiarize yourself with the Rider Swap/Switch program:
http://wdwuntangled.com/fastpass.php