Unless it's a particular look you're going for, it'll make your eyes look really bottom heavy and possibly make them look like they're drooping downwards. Extra padding on the bottom lashline can be aging - see those tele-evangelist wives for a fine example
A good rule of thumb is that whatever goes on the bottom lashline should be doubled on the top lashline.
I'd load up on waterproof mascara on the outer 3rd of your bottom lashline to give a bit of shape (and stop smudgies), but concentrate on bulking up the upper lashline with a good curl, loads of your favourite mascara and a few individual flare lashes on the outer 3rd. You can trim those to shape with some embroidery scissors so they don't have much length beyond your real lashes, but they'll fatten up the lashline and give a general impression of more lashes than you really have.
Have you ever had your eyelashes tinted? Some Japanese friends of mine with short, straight lashes swear by it, as the faux darkness of their natrual sparse lashes gives some definition and shape to their eye without needing to go overboard on mascara.