I'm afraid that the Gridseed "round stuff" (330-360 KH/s) is not going to be profitable if purchased at > $150, and even below $150 it's a risk since it can only do 1 thing - mine Scrypt. Of course it's all speculation, nobody can predict how difficulties, exchange rates, ASIC development, and everything else will evolve.

750 Ti is a fine piece of hardware, but it does use ~5 times the power of the Gridseed (not quite 70W, I think it's closer to 50W) and produces less hashrate, so it will become unprofitable much sooner. However it can do other things, such as Scrypt-N. Or play games. It will always have more value than a Gridseed. And there is no doubt that NVIDIA will come out with something more powerful based on Maxwell, which could make a difference.