Half of the time pictures and videos tend to fail getting sent over iMessage for me anyway, and they have to be sent as SMS. Not sure if this is an issue with my home WiFi, or Verizon, or what as I haven't paid that close of attention.
Either way 90% of the time I would be perfectly happy with getting a lower quality picture or video of whatever someone has sent me in a message. I don't need every picture my wife sends me of my daughter to take up 2-4Mb of my data plan (her sending it, me downloading it). But I would like to see what happened etc. My wife will have the full quality image on her phone and we will copy it to our computer and keep it there eventually. Same thing with other people, if the picture/video they sent me is that important there are other ways I can get it.