I definitely don't wait around when I can't find a group. But It's pretty ridiculous when I get 5XP from doing Black Talon/Esseles for the second time when I'm only level 15 and it's a 10ish flashpoint. (I know I could go do Hammer Station at 15, but that's not the point) Trust me, I'm not talking about being level 50 and wondering why BT gives me no XP. I did Foundry at level 42, I believe it's about a level 38 flashpoint, Why does a measly 4 level gap mean that I get practically nothing from it except XP from killing mobs? I The mobs weren't grey, in which case I would understand, and the bosses were still a pretty decent challenge, it's not like we ran through the place and powered through it in 20 minutes.
I guess it's more of a thing for going back and doing it for the sake of doing it I guess. Helping OTHERS who were in your situation maybe.
As for the 4 or 5 level gap, I don't understand it too much either. They can stand to make the whole "lol no exp" thing for when you're 10 levels above. That would definitely be enough unless for whatever reason there are several flashpoints between 45 and 50; in which case I'd understand due to being able to grind the lower level one easier if you were say, 48 or 49 at the time.
I'd actually like to see if Bioware has/will address that particular thought.