The 750 is a Maxwell generation GPU, it is much faster than the 730 which is both lower-end and older generation.
Your 3D animation software will use the GPU to render the live preview and depending on how complex the scenes you work on might get, the 750Ti might not be as overkill as it may sound. For the final rendering, the software may also use the GPU to accelerate rendering and compression.
For the amount of extra performance you get between the GT730 and 750Ti, I'd say "better safe than sorry" and vote for the 750Ti, well worth the $40 extra for over twice the performance. That makes you less than half as likely to need an upgrade and have to spend another $150 in the foreseeable future. If you can afford to wait, you could...