worst time of the year, as it is in most of Europe, hence the cheap flights. Short daylight hours and possibility of rain or even floods. But it's always a wonderful place to go, and there won't be millions of other tourists around and it won't be spifflicatingly hot as it may be in summer. Go for it!
just because you're visiting venice, you don't have to eat or sleep in venice; there are hotels & restaurants at Mestre (on the mainland end of the causeway) that are much better value - and it's only a cheap, short train ride away.