The issue I've found with splitting lengthy text messages is that there is not necessarily a standard amongst carriers as to a maximum text message length.
Usually, I receive lengthy text messages split every 160-180 characters or so. But I have a couple of contacts that have the capacity to send a single gigantic text message. I'm not sure if they're using a special app, or if it's their carrier, but I've gotten texts that were greater than 160 characters before, only from a few of my contacts though.
So maybe it'd be a good idea to have a toggle in the settings letting the user decided whether they want to split their long messages or ship them as a giant block. I don't know if this will be technically feasible, or if it'll be useful to anyone, but it'd be nifty.