Nope, it will still be a huge upgrade over your Intel integrated graphics. Graphics card performance should not be measured by how much video memory it has. Furthermore, the Intel integrated graphics uses system RAM as video memory, whereas the 750 Ti has its own memory (which is also a lot faster: GDDR5 vs DDR3). There's just no comparison between your current Intel integrated graphics and the 750 Ti.
If you're going the 750 Ti route, you won't need to upgrade your PSU. With a non-cheapo 550W PSU though, you can go as far as a GTX 680, but cards in this class are usually quite huge (10" or more). So if you're looking for a small graphics card, chances are, you won't be needing the PSU upgrade.